The Mars City Security mod adds co-op: in addition to playing through the campaign together, players can compete in several classic multiplayer modes. In its current state, the mod only adds the ability to complete PvE missions, and a full-fledged campaign co-op did not have time to appear - the authors abandoned it.

Development stopped in 2015, but fans of come on finalize it at the end of last year - they decided to add a full-fledged co-op to the game and refine the existing modes. It is not yet known when the fruits of their work will see the light of day, but the old version is available to play.