Blockland - Blockland is a non-competitive multiplayer sandbox-style construction game. It's kind of like playing with legos on the internet.
Xonotic - Xonotic is a free (GPL), fast-paced first-person shooter that works on Windows, OS X and Linux.
NERF Arena Blast - The website linked is not real page, just moddb page.
Quake - Quake is a series of first-person shooter video games released by id Software.
Blocksworld Wool - Download mods for Blocksworld!
Counter-Strike - Counter-Strike is a PC-exclusive FPS video game developed by Valve Corporation.