AssaultCube is a FREE, multiplayer, first-person shooter game, based on the CUBE engine.
Taking place in realistic environments, with fast, arcade gameplay, it's addictive and fun!
With efficient bandwidth usage, it's low-latency and can even run over a 56 Kbps connection. It's tiny too, weighing in at a lightweight about 50 MB package available for Windows, Mac and Linux. On the correct settings, it can even run on old hardware (Pentium III and above).
Important information for Windows 10 users: if you experience a mouse glitch (random camera movement), you can use the experimental hotfix for AssaultCube 1.2.0.2 on Windows 10. Note: the hotfix SHOULD NOT be used to competitive play and mapping - see known issues.
Most of this README was directly copied from the AssaultCube Homepage, which should have everything you need in relation to AssaultCube.
You may redistribute AssaultCube in any way the license permits, such as the free unmodified distribution of AssaultCube's source and binaries. If you have any doubts, you can look at the license.