Killing Floor 75% off again, and more
This game was 75% off many times within the last few months. Anyone who doesn't own this game for some reason should get it now. $5
And there's an official Halloween event going on as always. Tripwire is more involved with the community than pretty much everyone else. In fact, you can get every Tripwire game for $25 lol.
The entire Penumbra franchise is on sale for only $2.49.