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Obsidian Conflict is a co-operative modification created for Half-Life 2. It is a community based mod with focus on fun, co-operative and physics-related puzzles. The mod has an open story, but is still set in the Half-Life 2 universe.

Pájaros de Barro is a Spanish Gaming Community which offers public servers and support (tutorials, videos, forums, articles…) for Team Fortress 2 and Left 4 Dead as well as updated and fully spanish translated news and interviews related to Steam and Source Engine based games.

Phenomena On Break is a community brought together by their love of Valve games and games in general. They have used Valve games for over a year to make over one hundred comics based in the Half-Life universe, as well as the use the Source Engine and Gmod to create original universes and characters. They [...]

Steam Friends covers all the news related to Steam and Valve.

The Snarkpit has been online since 2001, making it one of the longest running websites that covers Valve’s games. It has had a number of redesigns over the years and always adds new features.

The Whole Half-Life AKA TWHL is first and foremost a community of mappers and modders. It has very active forums and plenty of tutorials.

Valve-ERC Forums is a forum for mapping and modding, focusing on Source and GoldSource issues. The Half-Life 2/Source section is outdated because it moved to a sub-forum of the SteamPowered forums.

Zombie Panic: Source is a survival horror MP HL2 modification. Play as either the survivors or the undead, trying to wipe each other out or completing objectives to escape the horror.