With a lot of new members not knowing how our base community had evolved we started out pooling together in the beginning playing Sven Co-op together.
Sven Co-op (www.svencoop.com) turns Half Life 1 into a Cooperative Multiplayer and from that it has created one of the biggest fan based games ever with thousands of user maps and custom content... sven Co-op was created by SvenViking from www.svencoop.com as a way to allow friends to hang out together and enjoy playing the Half Life story line together along with some custom content which grew with each release!
For those that do not have the original half life game you can purchase it for $9.99 via Steam Store http://store.steampowered.com/app/70/ I do not recommend buying it unless you watch some video's of how Sven Co-op is played and see if you like how it looks as it is not the same experience as the way Source games look because it is an older engine that had been updated but still doesn't have the same look and feel but the mods like Sven Co-op do make it seem like its a lot more then it is regardless of what engine it is!
We have been hosting Sven Co-op since about 2002 and probably will continue hosting it for a long time to come!
Just in case your curious about purchasing Half Life and want more content for it you can check out other mods to use with it here at the Mod Data base http://www.moddb.com/games/half-life/mods