The multiplayer co-op game Dead by Daylight is currently half off for Halloween - until November 1st. Base game cost is usually $20. It's $9.99 til November 1st.
Link here: http://store.steampowered.com/app..._Daylight/
Freddy is scheduled to be released as the newest playable serial killer today - in celebration for Halloween.
Note: Although this game is also on Xbox, Microsoft does not appear to be participating in his sale... PC on Steam only so far