http://store.steampowered.com/app/113020/Monaco_Whats_Yours_Is_Mine/ Monaco: What's Yours Is Mine free for 1 day.
https://www.humblebundle.com/store/oddworld-abes-oddysee / https://www.gog.com/game/oddworld_abes_oddysee / http://store.steampowered.com/app/15700/Oddworld_Abes_Oddysee/ http://store.steampowered.com/app/308040/Back_to_Bed/ - http://store.steampowered.com/news/32781/ (limited for 2 days)
http://store.steampowered.com/app/38400/Fallout_A_Post_Nuclear_Role_Playing_Game/ Free for about a day
A.D. 2044 + Stronghold HD is free for 48 hours on https://www.gog.com/ Not a steam game, but free game regardless on different platform.
Guns of Icarus Online Free for about 2 days Star Wars: The Old Republic Rise of the Hutt Cartel & Shadow of Revan expansions, Swoop Bike Ends on November 6th.
If you guys haven't tried The Old Republic because you've heard bad things, I'd recommend giving it a shot. The class stories are great and the expansions keep getting better and better after each release. I say this as someone who's played the game since the shitshow that was the original 2011 launch.
https://www.humblebundle.com/store/killer-is-dead-nightmare-edition The killer is daed Nightmare edition is a free game. but 2 day left.
Marvel Heroes Omega is closing down on 31st December and thus they are giving away all the paid content in the game for free (1000 ingame currency a day and EVERYTHING only costs 50 currency so thats 20 heroes a day) the game is a fun little ARPG similar to Diablo and Grim Dawn. also you can get a potted groot soooo