Obsidian Conflict is a cooperative multiplayer modification set in the Half-Life 2 universe. It features a large amount of new gameplay features on all-new maps specially designed for the mod with focus on cooperative gameplay, as well as over hundred user-made maps following the same formula. In addition to that, You're able to play through vanilla Half-Life 2 all the way up to Episode 2, as well as experimental support for cooperative Half-Life: Source play.
Very Great mod! one of the best mods i ever seen.
Only thing holding this mod back (like most MP Source mods) are the exceeding amount of trolls on certain or various servers.
Good Examples: MGO Dissent and LevelNULL Servers.