Play the official Alien Swarm maps and any addons through the Offline Practice mode. Alien Swarm:SP also supports a large amount of configurable changes for mappers to help them create new single player maps for Alien Swarm. As the online community who play Alien Swarm seems to be getting smaller and smaller my hope is this mod will revive the game.
Ch1ckensCoop MapPack. Currently on my server. Unlike mappack 1.2 this contains the newer maps. I have NOT tested all of the maps, and i know some can cause crashes on my server. I am waiting for mappack 1.3 to come out by goodone, and hopefully it contains all of the newest maps, with the bad crash-causing maps deleted. untill then i will publish this for people who play on my server, so they don't have any problems with missing maps. This pack contains 62 campaigns, 22 pages in alien swarm.