Simultaneous Arcs

Let us say you have several different characters and each one has their own separate journey for at least a portion of the story. These characters may or may not meet up with one another later on, but for now they are all on their own and their journeys, while they may be related, are independent of one another at least for the time being. There are two ways of handling this: One way would be to tell every single event in chronological order, frequently cutting from one character to the next, and then to the next as each event plays out. This first method would be known as Two Lines, No Waiting. For obvious reasons, stories told in Real Time would have to do it this way.

For stories that are not told in Real Time, however, there is another option. That option is known as Simultaneous Arcs.

Lets say you have two different characters: Alice and Bob, and these characters are separated from one another and are doing their own thing for a while, but each one is doing it at exactly the same time as the other one. It would work something like this:

Chapter 1 takes place between 1:00pm and 2:00pm and includes everything that happens to Alice during that time period without regard to what Bob is going through.
Chapter 2 also takes place between 1:00pm and 2:00pm, except it is told from Bob's point of view and has absolutely nothing to do with Alice

This process would be repeated until Alice and Bob meet up.

This differs from Rotating Arcs because Rotating Arcs is a method of dealing with Loads and Loads of Characters and the arcs occuring in Rotating Arcs don't have to occur at the same time.

This is similar to Anachronic Order, except the events in each arc of Simultaneous Arcs are probably told in the order that they occur from the point of view of the character and it is the arcs themselves that are not in chronological order.

This can sometimes result in a Mind Screw, but it usually won't.

Compare Hyperlink Story. Can be related to The Rashomon and POV Sequel.

Examples of Simultaneous Arcs include:

Anime and Manga

The Hueco Mundo and Fake Karakura arcs for Bleach. One is a Rescue Arc, the other is a Big Badass Battle Sequence.
The first two episodes of Speed Grapher occur at roughly the same time. Episode One is told from the point of view of Saiga, while the second being from the point of view of Kagura, and both have roughly the same climax. The rest of the series is mostly told in Chronological order, with the exception of a few flashback episodes here and there.
Boogiepop Phantom is a possible example. In general, the whole anime is a complete Mind Screw and it's extremely difficult to determine when exactly certain events took place or even to get a decent grasp on what is actually going on. There are several events that are shown multiple times, however, and each time it is shown, it is from a different perspective.

Comic Books

Sin City's characters often run into each other in the middle of their respective stories at Kadie's Bar.
Invincible has the Sequid arc (starring Invincible, the Immortal, Atom Eve, Robot, and Bulletproof) simultaneously occurring with the Lizard League arc (starring Rex Splode, Dupli Kate, and Shrinking Ray).
Uncanny X-Men had a example of this trope in #274 and #275 with the Savage Land arc with Magneto and Rogue and the whole Shi'ar arc with the current team roster at the time trying to fight Skrulls. To be fair, this is during Claremont's 1st run which fits with his style.

Fan Works

Turnabout Storm's trird part is divided into 2 videos, one showing the investigation from Phoenix's P.O.V., and the second one from Twilight's.

Film

The events of Saw III and Saw IV occur simultaneously.
Each of the characters stories in Hoodwinked.
The plots of the four main characters in 4.3.2.1 are told this way, with onscreen captions telling us what time and day it is so the audience can keep track.
Go employs four simultaneous storylines: one with a group of club kids, one with a drug dealer enjoying a weekend in Las Vegas, one with a pair of soap opera actors, and one with a narcotics officer. Some stories start earlier, and others finish later, but they overlap and intersect in several places.
The money drop scene in Jackie Brown.
During the racetrack robbery in The Killing the perspective of the characters involved in setting up the robbery are shown.
This is the main conceit of the 2000 drama Timecode. The film (presented as four separate unbroken takes in a single screen) follows several different people, including an actress, her lesbian lover, a casting director and his wife as they go about various activities over the course of the day, and occasionally intersect with one or more of the other arcs.
In the Marvel Cinematic Universe, the events of Thor, Iron Man 2 and The Incredible Hulk take place during the same week. The tie-in comic Fury's Big Week also takes place at this time.

Literature

Stephen King's The Stand is mostly told in chronological order and most of the chapters are relatively short. However, in the first half of Book Two, after the Superflu has wiped out 99% of the population, each one of the main characters or group of characters gets their own large chapter all to themselves, detailing their own journey as they cross the United States.
The Piers Anthony Incarnations of Immortality books use this trope. The most complete version of this trope is in the book For The Love Of Evil which shows Satan's view on the events.
The Lord of the Rings - The Two Towers portion of the novel is divided up into two segments (as the other two are), the second one detailing the journey of Frodo, Sam, and Gollum to Mordor, and the first segment is about Aragorn and everyone else in the book. The Return of the King does the same thing as well, though not to the extent of The Two Towers. The movie adaptation does away with this and instead uses Two Lines, No Waiting.
A Song of Ice and Fire - Many chapters occur at the same time as other chapters, and the first 800 pages of A Dance With Dragons will take place during the same time period as A Feast for Crows.
In Jean Auel's Valley of the Horses, the chapters alternatively tell the story of, on one hand, Ayla, and on the other, Jondalar and his brother Thonolan as they travel across Europe. Only near the end do they merge as the brothers reach said valley.
Lemony Snicket Book the Twelfth. The Penultimate Peril has simultaneous arcs with each of the three siblings, which is especially confusing when they each meet one of the twins at exactly the same time.
In Treasure Island, while Jim Hawkins is on the island witnessing Silver's murder of one of the last loyal crewmen, and then meeting Ben Gunn, three chapters are narrated by Doctor Livesey detailing the departure of the officers from the Hispaniola, the setting of camp in the old stockade, and the death of Tom Redruth. Just as Captain Smollett is setting down to write his log, Hawkins returns and resumes the narrative for the remainder of the book.
The Double Diamond Triangle Saga. Forgotten Realms series of nine novels, with the plot threads approached in different context depending on the order in which you read them (as seen here - arranged in, well, Diamond + Triangle). This was done after The Green Mile attracted attention, possibly trying to capitalize on the new "thing", but this format gives interesting possibilities for Gambit Pileup in the setting notorious for those. Alas, this project was doomed by obvious mismanagement.

Live Action TV

Are You Afraid of the Dark? did this in the episode "The Tale of the Silver Sight." The Midnight Society was looking for pieces of an old record to solve a mystery, and each member had one piece to find. It would then show one character's arc at a time, and would loop back to the same scene of everybody meeting up in Gary's dorm room, before going back to another person's scenes.
Coupling does this in a few episodes. 9 1/2 minutes (The first of season 4) is probably the most obvious example.
Lost has done this in increasing amounts since season three. Episode 3x01 tells what's happening to Jack, Kate, and Sawyer after the season 2 finale. Episode 3x02 shows what's happening to Sun, Jin, and Sayid. Episode 3x03 shows what's happening back at the beach camp with Locke and others. Season five has delved into this style even further, with some episodes focusing only on those still on the island and others focusing entirely on those who left (though "simultaneous" is somewhat a relative term when time travel is happening.)
Battlestar Galactica did this in Season four with Sine Qua Non and The Hub, which first showed the Fleet's story, and in the next episode the base star's simultaneous adventures.
CSI "4 x 4"
Dollhouse "A Spy In A House Of Love"
Some of the events depicted from Spike's perspective in the Buffy the Vampire Slayer episode "Fool For Love" are shown from Darla's in the Angel episode "Darla" (which originally aired back-to-back with it).
- Also done in "Same Time, Same Place", when Willow returns to Sunnydale but is invisible to her friends (and vice versa). All scenes in which She, Buffy, and Xander are in the same place is first shown from one perspective, then the other (usually with a clock or section of third party dialogue to orient the viewer)
This happens in the Smallville episode "Promise" (season 6, episode 16), which shows the same day from the perspectives of Clark, Lex and Lana, all of which converge near the end of the episode.
The Sarah Connor Chronicles episode "Mr. Ferguson is Ill Today", the episode where the protagonists finally succeed in destroying Cromartie's chip. One of the more well-done episodes of the series.
A season 3 episode of Alias did this: the first half followed Sydney and Vaughn around, while the second half repeated the first half's events from Sark and Lauren's POV.
New Zealand's Outrageous Fortune and probably Scoundrels.
Frequent device on How I Met Your Mother. It was first done in the season 1 episode "Cupcake" with two threads as the group is split between Marshall at a tailor and Lily shopping for a wedding dress. The technique's been used several times since but its more common form in the show was first exhibited in the early season 2 episode "Brunch". In this episode there are three groups rather than two and the contact points before the last one are actually different parts of the same event, as well.

Video Games

BlazBlue: Continuum Shift has the characters' story routes operate like this.
The Siren games follow this trope nicely, each game consists of around ten different characters experiencing the apocalyptic events simultaneously over the course of a few days and the story is told through snippets of the story told out of chronological order via a little timetable style level selector. Being told like this the story is very hard to follow at times and very disjointing when one minute your playing Kai on 'day 3, 10:00am' then suddenly your back to day 1 morning. Once you do have a dencent handle on the story though it is pretty rewarding.
Half Life and its two expansions, Blue Shift and Opposing Force, all take place during the same incident, with different heroes. Opposing Force has Shepherd's story begining partway through the original game, but we do get to see what happens at Black Mesa after Freeman is transported to Xen. In Half-Life: Decay you play as two characters during the events of Half-Life.
Resident Evil 2 was popular for its two-disc "zapping" system. You'd play through the game with one character, then you could start a New Game+ with the other. The game treats the two playthroughs as simultaneous, intertwining stories, and the things you did on the first playthrough affect the world in the second. In addition to this, the events of Resident Evil 3 take place in the same general area, with the events of the second game taking place within the timeframe of the third.
Most iterations in the Sonic the Hedgehog series, especially from the Dreamcast forward. The original Sonic Adventure is the most fundamental, straight version of the trope, but Adventure 2 is particularly notable in that the two stories are actually the opposing sides, not just different shades of heroism.
Front Mission 4 is played in chapters alternating between two different teams of pilots in completely different locations. The story occurs chronologically, but the characters don't meet until the very final chapter.
~11eyes~ has Cross Vision mode, where the same stretch of time can be revisited from the perspective of another character. Sometimes the events overlap, but a lot of the time a completely different side of the story is being shown. Heroes and villains alike let the player see their side of the story.
Kingdom Hearts 358 Days Over 2 takes place at the same time as Kingdom Hearts Chain of Memories from Roxas's point of view. It starts not long before the events of Chain of Memories and continues until just before Kingdom Hearts II when Roxas fights Riku and loses, which then kicks off the prologue of KHII.
- Chain of Memories also has a mode where you play as Riku in the castle basement instead of Sora.
  - And right after Sora reaches the top of the castle, Riku reaches the main/front door of the castle.
Raw Danger deals with several survivors of the flooding of Geo City all taking their own individual paths, usually barely meeting each other at all.
The first mission of the first Medal of Honor occurred at the same time as the mission "Rendezvous With The Resistance" in Allied Assault.
Pretty much the entirety of Treasure of the Rudra.
The initial part of Suikoden III is told in chronological chapters from the perspectives of three lead characters who begin in separate locations but frequently interact. Each set of chapters covers roughly the same period of time, allowing you to view some events from multiple perspectives.
Grand Theft Auto IV and the episode packs for the xbox 360 all occur at the same time, with missions sometimes occuring from a different point of view, such as Elizabeta's coke deal that with Johnny and Niko, or Johny and Luis and the Diamonds.
Aliens vs. Predator 2: The Alien causes infestation of the main Mega Corp base. Marine comes to investigate and inadvertently disables the other base's security, causing the Alien to attack it. The Marine gets captured by the Mega Corp, escapes, and unwittingly frees the Predator who you got captured as earlier.
- in the 2010 game, the Marine character watches the Predator character's ship blow away the USS Marlowe and fights to the colony, following a distress signal triggered by the Xenomorph character's escape. The stories diverge until the Marine character kills the Xenomorph Matriarch, upon when the Xenomorph character develops into another Matriarch. The Marine then fights Karl Bishop Weyland, while the Predator kills a Predalien and rigs the temple to self-destruct.
Operation Flashpoint's Cold War Crisis campaign covers the same conflict from four different character's perspectives, in chronological order. There is a lot of overlap in the events, particularly towards the end. For example, in one mission, where you play as a special forces saboteur, the number of enemy tanks you manage to sabotage is directly linked to how many tanks you face in battle the next day, where you play as the tank commander character.
Remember 11 uses this, with the entire story being told first from the perspective of Kokoro, and then restarting from the beginning, seen through Satoru's eyes.
Dreamfall shifts its narrative between three main protagonists, Zoe Castillo, April Ryan, the protagonist of the first game, and the elite Azadi soldier Kian. The three characters cross paths several times throughout the game and end up all coming together to some extent towards the climax.
Some of the Tortage quests in Age of Conan work like this, where different class archetypes do quests giving different perspectives on the story.
The second Tenchu game operates like this. Only by playing through multiple times can you get the full story.
Odin Sphere has all of the characters' stories take place in roughly the same time. There's even a handy timeline showing all cutscenes and levels together for orientation. All of the arcs lead up to the final epic battle involving every playable character.

Webcomics

The Law of Purple has a short side arc, focusing on a minor character, set during a major battle. As seen here.^{[dead link]}
Usually happens in Sluggy Freelance whenever a main character is trapped in Another Dimension, or back in time, or in an underground Egyptian tomb (this sorta stuff happens to them a lot).
Order of the Stick did a story in which Nale switched places with Elan; after the switch, Elan and Thog were put in jail, after which the comic followed Nale's infiltration of the Order over about four days of in-story time, leading up to an attempt to murder Haley - at which point Sabine rushes in, and then Elan and Thog crash through the window. The very next strip rewinds to when the twins switched places, but this time follows Elan and Thog as they escape from jail, Elan literally takes a level in badass, and they track down Nale, culminating in them jumping though that window.
A storyline of College Roomies From Hell! does this, following one character at a time over the course of the same week. It's kind of confusing until the end, but awesome nevertheless.
Book Eleven of Schlock Mercenary involves the crew splitting up to raise money for repairs, but early on, the Lemony Narrator informs us that in seven hundred or so hours, they will be summoned back following an ominous call from Petey to Kerchak. Each of the Toughs' groups then have their own story, with the Narrator frequently butting in to inform us the exact time until the fateful call occurs.
El Goonish Shive a few times, the big one in the Grace's Birthday Party arc - splitting up the characters into pairs and telling their stories one at a time.
Girl Genius often overlaps Rotating Arcs, with protagonist and her suitors, rescuers and/or antagonists facing various problems at the same time, while one tries to find another.
Sinfest often delves into this, most notably the recent separate arcs regarding the Patriarchy, and the developing love story between Criminy and Fuschia.

Western Animation

South Park had a three-part meteor showers arc, each episode told from a different point of view: Stan got one, then Cartman got another, and then Kyle and Kenny got one as well. Each episode is completely different and the only thing they have in common is the meteor shower.
The Simpsons, "Trilogy of Error": Each of the show's three acts follows Homer, Lisa and Bart respectively as they go on simultaneous adventures, which occasionally cross each other before meeting at the end.
Chowder "The Wrong Address/The Wrong Customer": During "The Wrong Address" Chowder and Mung see a seemingly insignificant police chase and go about their business. At the end they return home to find it destroyed and Truffles being arrested. In "The Wrong Customer" we find out that the police were chasing an old owl, who causes Mung's place to be destroyed. Truffles being arrested is a seperate but somewhat related matter.
Phineas and Ferb also did this. One episode had the boys building a bubble type contraption after sending the Fireside Girls to go get some sap. The next episode showed the girls' POV: their adventure as well as that of a different secret agent.
Transformers Prime has the hunt for the Iacon relics arc in season two—the episodes "Tunnel Vision", "Triangulation", "Triage", and "Toxicity" all happen at the same time. For bonus points, each episode has some scenes set back at the Autobots' base with Fowler and Raf, and Toxicity shows all these scenes in context.