List of good games

Battle for Wesnoth is the superior free turn based strategy game.

Oh, and I would also add:

Oolite, which is an Elite remake. It is a simplistic 3D space trading/fighting simulation.

FooBillard - 3D OpenGL billiard game.

TORCS - Racing simulation. You can also program robots to drive (in C++) and then race against them or participate in robot championships.

This hasn't been added yet:

BZFlag - free multiplayer multiplatform 3D tank battle game

Here is a nice list, that shows if it is GPL'd too...

Armagetron Advanced - a TRON clone in 3D

Stepmania and pydance are both good DDR simulators.
Stepmania is released under the X11 license

Warzone2100 is a classic RTS game which is now free'd by its developers.

This is a ported version to SDL which works under GNU/Linux. The original version, which only works with Windows and DirectX, can be downloaded from here. This package contains some source data so it may be useful to those who wants to modify the data.

Tremulous a 3D Quake 3 based first person shooter under the GPL.

So it's like Cube, it has nonfree data.

Damn

I don't play a lot with Linux, mostly a round of chess. For this I use Knights as frontend and gnuchess and the free version of sjeng as backends.
The other games I like to play from time to time are the old Ultima-games, which, of course are not open-source, but run nicely on Linux with Exult and xu4. And I'm still looking for engines for the other Ultimas.
If somebody knows about a really cool FLOSS RPG for Linux please let me know.

nethack - really cool FLOSS RPG

Already tried nethack some time ago. Somehow didn't want to compile. Maybe I'll check again.
Heard there's even some nice GUI for that, so that it doesn't look so old-school.

Personally, I prefer nethack without GUI but with color enabled. It's quite like a book without illustrations is better than a book with poor illustrations.

As I said, I never managed to compile nethack, but when it does I'll absolutely try out both versions. And if I don't like that "Falcon's Eye" stuff I'll stay with the shell.
It's not like I must have a GUI for everything.

pydance's license is a simple license similar to a BSD one.

I'd have to say:

abuse - I played it for like 30 minutes and gave up. It's tough, but it appeared to not be too tough. I showed it to my son and he loves it to pieces. He likes it to be tough because he gets bored with it, otherwise.

On Ubuntu I enabled universe and grabbed it with 'apt-get install abuse'.

P.S. 

Didn't see the rules on this thread until just now. Okay, I'm game.

Abuse is some sort of kill-the-monster kind of game where you see the game from the person's right or left, sort of like Mario Bros. You have a weapon and you get to jump and crawl around in tunnels. The monsters come at you fast, though, and they're fairly ugly looking and usually some kind of black slimy spider kind of thing.

It's not 3D, but 2D.

Abuse is a lot easier if you give either the keyboard or the mouse to someone else.

Ooh, some of these games seem to be pretty good, going on my install, at least most of them are

It seems that iD have released the quake 3 source code now

Although I may be wrong.

That happened long ago actually. There are already some games using the Q3 source.

...and even before that happens, most of the parts of the Quake 3 engine (except the computer AI) are already resembled by the community.

However currently the biggest lack is not codes, but game datas.

XTux - A 2D shooting game which features many free software characters

Nobody listed OpenArena and it really deserves a mention. It is a completely free FPS game (as in speech and cost) with everything that original Quake III Arena had and soon probably even more. Some effects actually seem even better than how I remember them on the original Q3A.

For everyone who likes that style it's a great game, right next to Nexuiz.

not sure about GPL, I think it is but VDrift is an AMAZING drift racing game.

I guess I'll try it sometime.. I currently have only TORCS installed of racing sims.. Nice one too.