Woah! That came as a surprise... I thought that Black Cat games had stopped work on the Source version of Alien Swarm (iirc, once called Alien Swarm: Infested) due to lack of interest, RL concerns, and all the other stuff that breaks up mod teams. Nice to see that they were actually working at Valve during the past few years. Downloading.
Hit And Run Poster Extraordinaire
--Too Dumb to Quit--