Then: Online Shooting: Doom (PC)

Doom is one of the forefathers of online multiplayer. The game's Deathmatch mode pits one user against another in a battle of total domination. If you somehow missed it the first time around (way back in 1993), you can download it through Xbox Live Arcade for 400 Microsoft Points ($5) and mow down your friends with a chainsaw. It's a great way to get rid of unwanted stress.