Half Life:Sven Co-Op

It's free and half-life, so needless to say, it's a great game, you can also play it over the network. Sven Co-op is a cooperative game originally based on Valve Software's Half-Life game.


 In this game, players must work together against computer-controlled enemies and solve puzzles as a team.

  Sven Co-op is similar to Half-Life with similar weapons, monsters, and characters, but the difficulty has been increased to accommodate team play.

  Sven Co-op's levels are tasked and generally separate from each other.  Many missions span multiple maps, and some are grouped together into a series.  The goal of most levels is to reach the end or achieve a goal;  Getting a high score isn't necessary to pass a level, it's just part of the fun.