Mod DB is the largest website dedicated to supporting independent development of games

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.

SLUM is Czech Steam community and fan portal about Steam and Valve games.

Solid Surf is a site specific to the surfing aspect of Counterstrike Source.

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

Stu-Pidaso is a website aimed at Half-Life and everything related to it.

TF2 Maps is a community mapping site based around an active forum. It offers map downloads, tutorials, servers, developer blogs and user galleries.

TF2Portal.es is a spanish website focused on Team Fortress 2. Some of the contents are: news, downloads, tutorials, forums and a public server. TF2Portal.es es una web en español dedicada por completo a Team Fortress 2. Algunos de sus contenidos son: noticias, descargas, tutoriales, foros, y un servidor público.

TF2 Tactics contains downloads, exploits, tutorials, skill videos, tips & tricks and training information for TF2.

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.

Tweak Guides provides incredibly useful information and tips on how to get the most out of your hardware and games.