List any good games that are free and native to GNU/Linux with a short description. If the game isn't 2D, say so.

Warning: Cube and Sauerbraten are not free software!
Some of their data isn't free.

Please, if anyone knows of RTS games like Starcraft and Warcraft (I know about FreeCraft), post!

Nexuiz (installer)- Fast-paced 3D multiplayer-only first-person shooter based on a vastly improved Quake I engine
Frozen Bubble - Puzzle game where you shoot three or more bubbles of the same color (or marking for colorblind mode) together to make them fall. The objective is to make all bubbles fall.

Well, I'm working on a project which is all about machinima (movies made inside video games).

Kenta Cho is most famous for this top-down shoot'um ups. After checking out the ubuntu repo's, i noticed that there are a whole bunch of his games packaged and available.

Let's not wait much longer.