Free co-op games that aren't first person shooters and don't suck?

Transformice is a neat puzzle platformer.

Duegon fighter online ,age of empires,dc universe online

nobody mentioned Hidden & Dangerous Deluxe, its free and they say it has COOP. If you got the money then buy Hidden & Dangerous 2

Company of Heroes. WWII at its best in video games.

Dungeon Defenders or Magicka.

I know people don't like Dungeon Defenders because of the large amount of DLC but you need to understand that you're not obligated to buy them, just having the base game is fine as a start. It's a great game to play with friends and getting better loot or beating the tougher difficulties adds to the re-playability.

Magicka is basically the same, the base game is enough to get started and the DLC adds to it but not required. This game also has a ton of DLC and most are just PvP levels.

Not free, but VERY good and not yet mentioned:

• Greed Corp - online/local, awesome turn based strategy.
• A Virus Named TOM - currently only local, great action-puzzler.
• Delve Deeper - local surprisingly good turn based strategy.
• HOARD - online neat dragon-action-strategy.
• Terraria - I don't even know, how it's possible, that no one mentioned it yet. online sandbox-rpg time-devourer.

EDIT:
Also super-duper-mega-awesome game - Torchlight 2 with online co-op coming really soon!! :D

EDIT 2:
Short, free, funny games:

• Mari0 - Mario meets Portal featuring local co-op.
• Block Breakers - nice action game with local co-op from DigiPen.

Trine 2.

Warframe, looks nice and I'll play it...I also made a thread about it a week ago clicky