Adapt or Perish, the latest game from Phr00t's Software is officially out today. It's an open world RTS with a huge amount of customization thanks to your ability to design your own units.
Releasing sometime later this year, the satirical office life simulation tycoon game 'Office Management 101' currently has a demo you can try out on Linux.
Megaquarium is a really lovely building game and the latest update has expanded a number of features, including the ability to fully customize how you play it.
One Step From Eden fuses together deck-building with plenty of customisation and some fun looking action, it's also managed to get fully funded on Kickstarter.
1001st Hyper Tower from developer Toster12D3 seems like quite a unique FPS, like a reverse dungeon crawler as you ascend a tower a destroy everything in your way.
I might be totally sold on this one already. Chained Echoes, a retro-inspired RPG which crashes magical and mechanical worlds together is seeking funds and it will support Linux.
BulletRage, releasing later this year is a twin-stick shooter from Chimera One Games that promises non-stop action and I've had a play with a preview build.