Converging Stream Weapon

This is a heavy weapon which contains multiple smaller devices that send out a stream, beam, blast, etc.. Those all converge into a single stream, beam, blast, etc., that is more powerful than the sum of its parts.

Usually, the resulting stream goes in the logical direction -- that is, in the direction produced by taking the average of the directions of the intersecting beams (although more advanced versions are able to swivel in any direction).

Besides Rule of Cool, this kind of weapon has grounding in conceptual mathematics. If lasers could add in the way vectors do, the result would be a laser of many times more magnitude than if it were simply fired from a single barrel (that is, the resultant beam travels several times faster than the speed of light). Fortunately for unexploded planets everywhere, this is not the case.

The inversion of this trope, where one attack splits into many, is Recursive Ammo or Spread Shot.

Compare All Your Powers Combined, Roboteching, Wave Motion Gun.

Anime and Manga

 * The "Dark Star Weapons" in Slayers Try function in this manner. At the end of the season, all five weapons are combined with a Yin-Yang Bomb into a Wave Motion Gun.
 * The "Precure Marble Screw" attack from Futari wa Pretty Cure is like this.
 * Used in Rebuild of Evangelion as Unit 1 fires the Positron Rifle at Ramiel.
 * The Transformers Energon incarnation of Optimus Prime can normally fire Roboteching Beam Spam. When combined with Wing Saber he can perform a Combination Attack with the Attack Drones which would normally form the limbs of his Super Mode - "Meteor Attack Mode" consists of him firing a Chest Blaster at the same time as the normal beams, which absorbs them to create a massive stream of plasma.
 * Although it was only used twice, in Legend of the Galactic Heroes the ships of a fleet can fire all their lasers in a "pinpoint attack" that spawns a super-beam that can decimate bunched-together ships.
 * There's also the Thor Hammer.

Film

 * The Death Star in Star Wars may be the Trope Codifier, if not the Trope Maker.
 * Subverted in this parody video.
 * The clones' helicopter gunship analogues were later shown with a turret-mounted weapon that worked similarly.
 * Reign of Fire: The dragons produce two chemicals in their body that are exhaled and combine to produce their fire; there is an actual animal that does exactly that.
 * Ghostbusters: "Do not cross the streams." But they end up doing just that. And they don't cross, they, well, converge, hence why they're here.
 * The motherships' primary weapon in Independence Day.

Literature

 * The upgraded Slaver Disintegrator in Larry Niven's Ring World, also known as the Wunderland Treatymaker which crosses two of them with reverse polarity. Specifically, one beam suppresses the charge of the electron, causing matter within it to acquire a large positive charge (and tear itself into dust). The other beam suppresses the charge of the proton. When both beams are used, there is a current flow.
 * The Slaver Disintegrator uses parallel beams. The current flow happens between the impact sites, adding electrocution to the localised disintegration effects.

Live Action TV

 * On Babylon Five, Vorlon ships had several booms on the front of the ship that each emitted a lightning bolt - like beam. They met in the middle to create a Wave Motion Tuning Fork effect.
 * The Interstellar Alliance's Victory-class destroyers (which were based in part on stolen Vorlon technology) used beams sent from the three wingtips to the front to convert the entire ship into a massive Wave Motion Gun.
 * In Star Trek the Next Generation, the Federation developed a 'collimator beam' made of dozens of small phaser banks spread along the rim of a ship, the energy can be seen flowing along the surface of the Enterprise until it meets at one point, and then fires off from the point on the phaser bank row closest to the target.
 * On Star Trek Voyager, Species 8472 has a weapon consisting of several ships that acted like the Death Star when firing simultaneously.
 * The basic enemy fighter ship in Kara no Messeji: Ginga Taisen did this.
 * Several Power Rangers weapons work by this, the first being the original Rangers' Power Cannon from season two (one barrel fires five energy balls... that turn into one much more Badass one.)
 * The weapon Torchwood use against the fleeing Sycorax ship in the Doctor Who episode "The Christmas Invasion".
 * In "The Poison Sky", a similar weapon is used by the Airborne Aircraft Carrier the Valiant to fight off the Sontarans.
 * The Eye of Ra (the Wave Motion Gun Anubis uses against Abydos) in Stargate SG 1 is one of these. This makes sense, since the entire episode ("Full Circle") is a huge Shout Out to/Affectionate Parody of Star Wars (particularly A New Hope), with Lampshade Hanging aplenty.

Video Games

 * Multiple Beam Cannon units from Command and Conquer 3 will sometimes do this.
 * The Ion Cannon also works in this manner. Unfortunately, this telegraphs the actual attack, enabling your enemy to sell all buildings in the target zone before the main blast occurs.
 * In Red Alert 3, the Athena bombardment vehicle features converging beams on its gun. Unusually, they emerge from the same point on the Athena and "sweep" towards to the target from the left, right, and top. Also, they're the targeting lasers - once they converge, the real weapon shoots down from orbit.
 * Xenosaga Episode I had the Rhine Maiden, a converging wave-motion gun comprising the Dammerung and four smaller vessels in formation.
 * Starcraft II's Void Ray is a new Protoss ship built by the Dark Templar which serves this purpose. The number of beams that converge actually increases over time, letting it be a much better weapon against targets that take a while to kill (though it's still damn good against infantry).
 * Wing Commander Prophecy was supposed to have the Tiamat dreadnought equipped with a version of the "fleet killer" plasma gun mounted in the Kraken, with the green glowing tips of the Tiamat's arms forming the beam, but technical difficulties prevented it from being implemented.
 * Bang: Gunship Elite has many weapons, one of which fires rapidfire bolts from the meeting point of three continuous beams that emanate from three prongs in front of the ship.
 * This looks to have been averted in Freespace 2 with the Sathanas dreadnought, which has four massive frontal arms, each with its own beam cannon. Until the end, when they're brought together to form a sort of wibbly wobbly Swirly Energy Thingy between the arms.
 * Many of the Polaris vessels in Escape Velocity Nova (most notably the Arachnid and Raven) do this with their pink fusion bolt thingies.

Western Animation

 * Though a case of All Your Powers Combined, not this, Captain Planet's summoning looks a lot like doing this with The Power of Friendship.

Real Life

 * Lasers sometimes have multiple sources, then focus them all together into one coherent beam on exit (particularly ones that are supposed to be stupidly powerful, but where mobility is not a concern, like in laboratories).
 * This is also the logic behind a phased array, we just can't do it with lasers... yet.
 * And a phased array laser would be called... you guessed it, a phaser!
 * An 'implosion bomb' uses multiple smaller explosions to set off the main charge.
 * Some radiotherapy devices used for treatment of highly localized brain tumors operate on this principle. The method is called "gamma knife radiotherapy". Basically, they send several hundred (usually over 200) narrow gamma ray beams into your head. Each beam is fairly weak and doesn't do much damage, but they all intersect where the tumor is located. * Sizzle!*
 * Though not a weapon, this is how inertial confinement fusion reactors are supposed to work - with hundreds of laser beams converging on a tiny spherical pellet of fuel, causing it to implode and ignite a fusion reaction.