0 A.D (Zero Anno Domini) is a real-time strategy game developed by Wildfire Games which has recently released the source code, thus allowing us to enjoy the game without having to pay anything. The game has excellent graphics which are unfortunately quite rare in the Linux world.
Since this game has very good 3D graphics, the requirements are kind of high too. The developers say that having an Geforce 4 or Intel 945GM graphics card or worse will give you very bad gaming results and therefore you are advised not to play the game if you have such a graphics card. Furthermore, it is recommended you have at least 1GB of RAM, especially to prevent huge compilation times (yes, you need to compile this game to be able to play it). And finally, the processor should be a Pentium 4 or higher and at least 2 GB of free disk space.