Ensemble Cast

In most cases, the protagonist is a defining element of fiction. It is he whom the plot revolves around and, usually, the one the audience is supposed to empathize with most.

However, some shows decide to do something different - There is no protagonist. The plot and its narrative don't revolve around a single, "most important" main character. Instead, it shares a cast of characters with (almost) equal screentime and importance to the plot. This is called an Ensemble Cast. This type of narrative is interesting because it highlights the relations between different characters by taking away the importance of a single character.

In addition, it allows the writers to focus on different characters in different episodes freely, without worrying about giving the main character not enough screen time.

Rotating Protagonist is a subtrope of this.

Anime and Manga

 * Baccano!, in the same way Pulp Fiction does it. There's no main character here either.
 * Discussed in the beginning with Carol and the newspaper vice president in their debate about which of the characters is the main character.
 * Durarara!! in the same way as Baccano. They're based on books written by the same author.
 * Fullmetal Alchemist (manga/Brotherhood version) starts out centered around brothers Edward and Alphonse Elric, but over time the cast expands to the point that the brothers share the same amount of screentime as Roy Mustang, Scar, General Armstrong, Ling Yao, and other protagonists.
 * From the beginning, Soul Eater has been as much about the Black*Star/Tsubaki and Kid/Liz/Patti teams as it is about Maka and Soul.
 * Legend of the Galactic Heroes. Hardly surprising, given just how many characters there are that it essentially has to do this to give anyone screen time. The clue's in the title, too.
 * Twentieth Century Boys starts out with Kenji as the protagonist, but after the events of the "Bloody New Years Eve" (which happens fairly early in the story), the focus spreads out evenly among the casts. Kanna has a more central role than the others, but not enough focus to call her the "protagonist".
 * Simoun collects over a dozen main characters with roughly equal screen time towards the end.
 * Azumanga Daioh definitely is an example of this trope. It mainly centers on the antics of the main cast without straying too far into one another. Arguably there are more Sakaki stories than anyone else, but it doesn't get to the point of her being the main character.

Comic Books

 * Justice League.
 * Watchmen.

Fan Fiction

 * Honorable Hogwarts did this to the Harry Potter universe, giving Loads and Loads of Characters roughly equal focus and Simultaneous Arcs.
 * Adult Stuck, a Fan Sequel to the above mentioned Homestuck, does this.

Films -- Live-Action

 * Pulp Fiction, considering all the protagonists follow their own plot and their ways only cross at random.
 * Inglourious Basterds. Despite the Basterds being in the title of the movie, it puts the same focus onto them, Col. Landa and Shosanna Dreyfus.
 * The movie Crash focused on several characters and the racial tensions between them.
 * The Social Network is a glowing example, to the point where the most likable character in the movie isn't even the guy featured on the poster.
 * Magnolia
 * Shoppen
 * Twenty One Grams
 * Babel
 * Many of the films of Robert Altman, especially Short Cuts, Gosford Park and Nashville
 * The Avengers. The lead characters first appeared in their own respective movies before teaming up for this one.

Literature

 * A Song of Ice and Fire has something like twenty-five viewpoint characters, and switches between them every chapter. The TV series does the same.
 * Another example is The Sound and The Fury, which has four viewpoint characters that each get equal time, and Faulkner has said that the actual "hero" of the story is Caddy, who is not given a viewpoint at all.
 * The Animorphs series features six characters who swap first person narrations between books. While you can argue that Jake is the central most character, there really is no true main character.
 * The first book of the Hyperion Cantos. All the pilgrims have equal importance.
 * Lonely Werewolf Girl and Curse of the Wolfgirl, while Kalix is the titular charcter, all the rest of the cast have equally important and almost seperate storylines. Especially noticeable in Curse where Thrix, and Malveria's story arc have no contact at all with Kalix's.
 * Stephen King has a couple of books that could arguably fit this trope, chief among them IT and The Stand.

Live-Action TV

 * Stargate Universe doesn't really have a single main character either. Dr. Rush is usually presented as the protagonist, but this may have more to do with the fact that his actor is the biggest name among the cast. You could easily claim Young or even Eli is the main character.
 * Lost is a borderline case. There is an Ensemble Cast, but Jack has a more central position than the rest (as was finally made clear in the last season). Just not enough to call him the "protagonist".
 * Modern Family really doesn't have a main character, and focuses on all three branches of the family pretty much equally.
 * Friends famously had six main characters, or two Power Trios.
 * Heartbeat originally focused on village bobby Nick Rowan, but as the cast changed and expanded, the show developed an Ensemble Cast.
 * Star Trek Deep Space Nine was one of these. Unlike the other Trek series where the focus was firmly on The Captain, DS 9 gave pretty much equal airtime and weight to all its characters from Rom on upwards.
 * Star Trek the Next Generation, too, though not to the same degree due to a small recurring cast. Nonetheless, the series was generally good about giving each of its main characters focus episodes.
 * Casualty: has a regular turnover of cast and no fixed stars so everyone gets a storyline.
 * Allo Allo: Started with the focus on Rene, but the comedy hijinks and the sheer number of Once An Episode catchphrases necessitated the whole cast share the limelight (this is quite common with UK sitcoms, Red Dwarf, Are You Being Served, Dads Army, Mongrels et al all have an Ensemble to spread the weight and storylines.
 * Caprica has about four characters who could be considered the main character - Daniel Greystone, Zoe Greystone, Joseph Adama and Clarice Willow.
 * Community, although the pilot introduces Jeff Winger as the protagonist and the episodes with Two Lines, No Waiting generally have Jeff working the A plot.
 * At least on paper, Seamus O'Neill was the main character of Key West. And in the credits, it might have seemed that way. The truth was something entirely different, as O'Neill was actually very rarely the central character in any given storyline.
 * Parenthood
 * In Firefly, Captain Malcolm Reynolds is ostensibly the main character, although all of the characters get a significant amount of focus, and the River / Simon subplot is probably equally important to the main story overall.
 * The West Wing turned into this despite initially being thought of as being a show about Sam Seaborn. Led to a lot of cast/pay trouble.
 * Glee started out focusing mostly on a few characters (mainly Rachel, Finn, and Mr. Shu), but as formerly minor characters were given subplots and background characters became actual characters, the glee club, most of the teachers, and some students from other schools are arguably main characters.
 * The CSI franchise shows are all described as ensemble casts.
 * Criminal Minds rarely has ever had fewer than seven main characters. Notable exceptions were the episodes between Elle leaving and Prentiss joining, Gideon leaving and Rossi joining, and most of season six.

Videogames

 * Final Fantasy VI, though some members of the ensemble (Terra and Celes in particular) do get more screen time and Character Development than others.
 * The Subspace Emissary. Ultimately, the "star characters" are whoever you prefer to play as. Although the game does seem to feature Kirby, Dedede and Metaknight over the rest of the characters somewhat.

Webcomics

 * Rumors of War combines an Ensemble Cast with Rotating Protagonist (plus Two Lines, No Waiting and regular Time Skips) to create a Cast-Go-Round. The first and third Story Arcs mostly follow Elysia and Nenshe, while the second and (allegedly) fourth arcs follow Illyra and Occela. The characters also seem to spend a lot of time talking about things that happened in between the story arcs, with Obadai stepping in to provide advice and commentary.
 * Homestuck, thanks to its extremely large cast and tendency to switch between their points of view very rapidly. John is nominally the main character, but he is only the focus in the first, second, and fourth acts. The third (arguably) focuses on Jade, and John didn't even appear for the first part of Act Five.
 * El Goonish Shive tends to focus on groups of two or more more of the main 8 characters and a few supporting characters at a time.
 * Drowtales started off with focus on Ariel but the cast kept growing until there was 4-5 important story arcs running at the same time with equally important characters. Currently there was nearly a year where Ariel was never seen with more important plot lines hogging the pages. All those layers of plots of even greater importance that live in the background and probably will burst into foreground in the future.
 * The Inexplicable Adventures of Bob—While Bob is the main character (at the very least, because his Weirdness Magnet status drives everything else), the supporting cast gets a lot of screen time. Molly, Galatea, Roofus, Rocko, Jean, and Voluptua have each had story arcs focusing on them.
 * Goblins divides its focus between three groups of characters: the titular sextet of Goblins (of which none can be accurately called the main character,) Dies Horribly and his fellows, and Min Max and Forgath, a pair of human adventurers. All three groups are given roughly equal screentime, despite one of them not consisting of any goblins at all.
 * Charby the Vampirate confuses some new readers because while the comic is named after Charby, he's only one of many main characters. The story tends to rotate focus through the Loads and Loads of Characters.
 * Pv P has no single 'main character'.

Web Originals

 * Red vs. Blue has nearly a dozen main characters, most of whom have had at least a short story focused on them. If the series has a central character, it'd be Church (who is arguably indirectly responsible for almost everything that happens to them), but there's plenty of time in the spotlight for everyone else.
 * Every member of Team Kimba or Outcast Corner is a main character in the Whateley Universe, with now at least half a dozen more main characters added in. Every one of these is a protagonist of his or her own storyline.
 * Hardly Working stars all of the members of the College Humor editorial staff
 * The Descendants fields seven core characters with the focus in a given issue going to the older Power Trio or either Warrick or Cyn. The others get plenty of face time too, as do the supporting cast, guest stars and the occasional villain will snag a starring role for an issue.

Western Animation

 * Each of the three Total Drama seasons started out with several protagonists since the series is based on Reality Shows.
 * The show Archer, while titular protagonist Sterling Archer gets a fair amount of screentime, so do the rest of his co-workers at ISIS, often having their own plots.
 * In My Little Pony Friendship Is Magic, although Twilight Sparkle is clearly the main character, all of the Mane Six get a roughly equal amount of screen time and episodes dedicated to them. Especially during season two, where Twilight actually doesn't appear at all in a couple of episodes, or when she does, delivers a line or two.
 * The cutie mark crusaders also get the spotlight with a good amount of regularity and of them Apple Bloom has gotten her own episode and sweetie belle shared one with her sister.
 * The Justice League cartoon. Superman was sort of the "leader", or at least the League's public face, but he was never more or less likely to be an episode's main character than any of the original seven. Then the show went Heroes Unlimited.
 * The main six in Recess all get equal screentime. The creators said they wanted to do this to avoid the show becoming "The Gretchen Show", "The Gus Show", "The Spinelli Show", etc.