Utility Weapon

This is a video game gameplay trope where a weapon in the game can be used for something other than fighting enemies; typically by bypassing obstacles or being used to solve puzzles. This could be as simple as explosives (dynamite's a popular one) which can destroy specific barriers other weapons can't touch, however on the other end of the spectrum, Metroidvania style games often give the player equipment which allows them to bypass a given obstacle but also comes in handy against the various enemies the game throws at them (for example, a jump attack which allows them to both get over large gaps and to attack flying mooks). Another popular variant is to have the player's melee weapon be an Improvised Weapon which can also be used as originally intended (e.g. repairing things, cutting through barriers, digging etc).

The reason for this trope is often rooted in the constraints of a Game Engine. If the engine was originally designed for a purely combat based game and the developer wanted to make it more puzzle based (as was the case in the 90's, when the First-Person Shooter genre began experimenting with more story based games as well as RPG Elements) then they have to modify it. Since the original engine probably already allows the player to carry and use weapons, it makes sense (from both a technical and gameplay point of view) to create weapons which can be used in puzzle solving. Another good reason is that doesn't force the player to fumble around switching from "puzzle solving equipment" to "weapons" (thus averting a Scrappy Mechanic). The Action/Adventure (especially the aforementioned Metroidvania games) genre also favours this trope, since it allows the player to both progress through the game and be more capable of fighting enemies at the same time.

Note that a weapon being used to smash through barriers (or innocent furnishings) or do anything else which any weapon could achieve doesn't count; the utility effect must be unique to that weapon (or a couple of specific weapons). Nor do weapons which happen to be the weakness of particular enemies; those fall under Achilles' Heel. Supertrope to Muzzle Flashlight.

Compare Sword of Plot Advancement for when a weapon has a non-combat use in the plot rather than gameplay. Unintended examples of this trope (for example using the recoil on a weapon to jump higher) may lead to Sequence Breaking. Within the story of the game itself, the weapon might be an Improvised Weapon (if it's a tool which could normally be used to bypass the puzzles which the game allows the player to use as a weapon) or an example of Mundane Utility (if it's something made as a weapon which just happens to be useful for solving the game's puzzles). Also related to the Inverse Law of Utility and Lethality (where abilities and weapons are more useful when they're less effective at dealing out damage). This may also function as one of the Standard FPS Guns.

Action Adventure

 * The Metroid games run on this trope. The basic "Power Beam" doesn't do much outside of combat, however all the later weapons in every game can be used to remove certain obstacles and open colour coded doors.
 * Since every dungeon in The Legend of Zelda series contains one new piece of equipment (which will be needed to kill the boss and progress further) you can bet your last rupee that it'll have a use in both puzzle solving and combat (unless you end up against a Puzzle Boss, of course).
 * The LEGO series of games is full of these, practically every weapon in LEGO Indiana Jones is useful for something else (the wrench for repairs, the shovel for hidden items).
 * In Okami, Amaterasu's brush is used both as a weapon as well as pretty much everything else.
 * As with the Okami example, the brush in Epic Mickey serves as both a weapon and a tool (this time because of the ink based environment).
 * Cave Story's machine gun can be used to jump with the recoil.
 * Castle Wolfenstein.
 * Your pistol's bullets could not only kill enemy soldiers but shoot open locked doors (very useful if you don't have any keys) and speed up the unlocking of chests (better hope the chest isn't full of explosives like bullets or grenades).
 * Grenades can be used to destroy dangerous enemies such as SS troops. They can also be used to blow open locked doors and destroy interior walls and chests to make it easier to get around.

First Person Shooter

 * In Team Fortress 2, the Engineer's wrench melee weapon also repairs/upgrades his machines. In addition, several unlockable weapons can have other utility effects, such as;
 * The Pyro's "Homewrecker" allows him to remove Spy saps from the Engineer's buildings
 * The Scout's Force 'a Nature and Atomizer allows him to jump for a third time with the recoil.
 * Half-Life 2's gravity gun can be used to lift objects around (as well as punt them into enemies, of course).
 * In Clive Barker's Undying, dynamite can be used to blow open certain walls.
 * All Build Engine games (Duke Nukem 3D, Shadow Warrior, Blood, Redneck Rampage) have cracks in the walls that can be blown open with explosives. Explosives come in two varieties in these: a "rocket launcher" weapon a la Doom, and a ballistic thrown "grenade" or "dynamite" (Shadow Warrior has a grenade launcher instead).
 * The Unreal Tournament series has the teleporter gun, which shoots a projectile and allows to the user to teleport to it.

Platformer

 * Ratchet's wrench in Ratchet and Clank is a decent melee wapon, but is also used to operate a few mechanisms that resemble large bolts.
 * Duke Nukem II's flamethrower can be used to boost yourself up, like a jetpack.
 * The Apple II game Aztec (1982). The dynamite you found could be used to blow up enemies. It could also be used to blow holes in the floor, which could not only prevent enemies from reaching you but could also allow you to drop down to lower levels.

Puzzle

 * Rocks N Diamonds has a downloadable Zelda Level which has bombs destroy certain walls and objects

Role Playing Game

 * In Skyrim, mining picks (and other tools) are needed to carry out certain actions, but can also be equipped as weapons (indeed, some NPCs will use them as an Improvised Weapon).
 * Pokémon has Hidden Machines, which not only teach Mons attacks you can use in battles, but also outside of battles to bypass barriers. In addition, some non-HM moves like Flash or Headbutt can also be used outside battle but aren't typically needed to progress through the story.
 * In RHDE, the bat both breaks doors and damages enemy units.

Roguelike

 * In Nethack any item can be thrown at a monster or wielded and be used to bash a monster. While some non-weapon items will cause specific effects upon hitting a monster, there some weapon items that have non-combat uses:
 * Bladed weapons can be used to pry open locked chests, though doing this carries the risk of breaking the weapon.
 * Pointy or sharp metallic weapons can be used to engrave words into the floor, though this is slow and dulls the weapon. But an athame (a specific type of dagger) can not only engrave without becoming dull, but also engraves much faster than other weapons.
 * Wands of fire and lightning can be used to throw bolts of fire and bolts of lightning at monsters, but can also be used to burn words into the floor.
 * Wands of striking, in addition to being used to strike monsters, can be used to destroy statues and boulders.
 * Wand of cold can be used to freeze pools of water into solid ice, which is useful since your character comes with Super Drowning Skills.
 * Pickaxes and mattocks are considered weapons, but can also be used to tunnel through walls, destroy boulders and statues, dig pits in the floor, and dig holes through the floor which let you fall down to the next dungeon level.
 * A bullwhip can be used to pick an up off the ground if your floating or riding an animal, to fish on item out of a pool of water, or can wrap around a large object and be used to pull you out of a pit.

Survival Horror

 * Silent Hill Homecoming. The Ceremonial Dagger can not only be used as a weapon (doing more damage than the combat knife) but also to unlock certain doors and mechanisms, such as the Church Organ Puzzle.

Wide Open Sandbox

 * The Hookblade from Assassin's Creed Revelations is used for getting around the city and cutting folk up.
 * In Destroy All Humans!, the Anal Probe can (if used on a human when fully charged) cause the target's brain to pop out, allowing you to extract the DNA and use it to buy upgrades.
 * In the Rune Factory series, you can use swords in place of your sickle and your war hammers in place of your normal hammer (though not nearly as efficiently as the normal tools). This comes in handy in RF3, where using battle hammers during mining can yield metal ores like iron and copper more often than your leveled-up tool hammer (which tends to cough up jewels and crystals).

Non-Video Game Examples
"Maxim 44: If it will blow a hole in the ground, it will double as an entrenching tool."
 * While Real Life tends to be devoid of (deliberately designed) puzzles like the ones you'd find in games, certain objects which might be used as weapons (knives, small axes, entrenching tools) tend to be useful for more peaceful purposes.
 * World War Z gives us an axe that's also a shovel. So you can fortify your position and then kill the shit out of zombies.
 * Happens in Schlock Mercenary now and then. A plasgun doubles as personal thruster (it has a switch for thrust and recoilless modes) - and, of course, heavy-duty plasma cutter. Targeting systems of a whole load of missiles were used as an improvised sensor array (dubbed "Very Dangerous Array"), which later became standard issue.
 * Also, more general advice from The Seventy Maxims of Maximally Effective Mercenaries :