wait what's this?
Queeba gathers anyone from the BLF who can to a dedicated server of a mod that can run another game co-op and they beat the game together.
In this case, it's Half-Life 1 beaten through Sven Co-op, and now Half-Life 2 beaten through Synergy. Not yet beaten, but shortly in the future.
Also, Queeba, in Synergy, if I recall correctly, the citadel in HL2 and the episodes act a bit weird (also I think EP.2 is completely unsupported as well). Be cautious when playing it.