OrbiTank (AppID: 2074500)

Tanks! Space! Tanks in space!
Does much more even need to be said? OrbiTank is a local-multiplayer tank game with a fresh spin on projectile combat. Use gravity to your advantage to shoot your shells in and out of orbit, hop from planet to planet, and dive bomb your enemies. Explore a vast variety of arenas which feature several gravitational mechanics such as planets, orbiting moons, spinning space stations, and even treacherous black holes.

Classic
The classic game mode is good old reliable. You can't go wrong! It's just you, a friend, and the most balanced version of the game that has been experimented with. Players have three lives per round, and in order to win it all, you must rack up five points. Points are collected by winning levels, and levels will continue to be generated until either player wins the game. Usually a game in the classic game mode will last about 10 minutes, or until your friend starts to call your mother names.

Tournament
With the tournament game mode, you can challenge a whole group of friends to your mega epic gamer skills. Winner gets to not be made fun of for playing MOBAs. No, but seriously. Although no more than two players will ever be hashing it out on the screen at once, tournaments can be generated with up to eight contestants. This is a great game mode for parties and does not disappoint as a fun time sink. Expect hoots and hollers.

Custom
Trying to shake things up? Then this is just the game mode for you! You can modify several balancing settings using the custom game mode. This means if you want a really long game but it switches levels after every time a player is killed, you can do that. If you want to speed or slow down the fire rate to make the game more arcade-like or more tactical, you have the options. And, finally, my favorite, you have the ability to turn the planet movement up to like, a lot a lot. Prepare yourself for ludicrous speed.