SOS! Co-op players in need of sitrep!

So, it only just occurs to me now on Christmas day, that now is the best time to swipe a ton of cooperative games from the steam sales. The problem is, I can't for the life of me think of any good new ones.

Dear SteamGifters, your mission should you choose to accept it is simple :
Shout out the names of any awesome cooperative games you think that more people need to play. The more obscure and highly discounted the better, but even well-known recent releases and games that aren't exclusively co-op are fine too. I'll be peeking back into this thread during the day and will try to list the more tempting co-op titles just in case any of you want some new pixels to grind with friends and family.

JOLLY COOPERATION :
(no particular order, but numbered just in case you check back once more are added)
1) Tabletop Simulator - A simulated tabletop for boardgames and RPGs
2) Magicka 2 - Listed only because I'm an idiot and forgot that this was even released.
3) Killing Floor 2 - Well known quasi-arena vs-AI FPS that is still in Early Access, but already highly playable.
4) Earth Defense Force - Sadly not discounted this xmas, but may be worth wishlisting for when it is? Soldiers vs giant insects, woot!
5) Lovers in a Dangerous Spacetime - Cutesy space-survival local co-op, new and with fair discount!
6) Keep Talking and Nobody Explodes - A bomb defusal game where one person is the technician, and the other has to hurriedly give instruction on how to defuse, wither neither player having access to each other's information or screens.
7) Eon Altar - A single or multiplayer RPG that requires a smartphone or android device, which is used to manage your inventory and deal with personal matters such as levelling up... or dealing with private thoughts, hidden betrayal quests and so forth. Sure, you could tell your teammates you are here to steal the jade idol of Nogiranth, but what if they're here to destroy it? What if you want to use your current teammates as sacrificial pawns in a strategy to kill a king you have to talk with? Interesting concept.
8) Victor Vran ARPG - More arcadey, action, reflex take on the isometric combat RPG.