Swarm Keeper is a Dungeon Keeper inspired modification for Alien Swarm. It offers the following features: Build a dungeon for your creatures (aliens), imps which perform tasks for you (like digging blocks away, collecting gold), a portal through which creatures enter your dungeon, different room types (treasure, lair, hatchery and training), a dungeon heart, which must be protected from enemies and invading marines as enemies. This mod should be considered as an experiment to bring a Dungeon Keeper like game to the Source Engine.
Swarm Keeper 0.45: the game now allows you to drag an area to create a room (including a preview), shows the max gold and player tiles are now team colored.
This is turning out quite well!