I noticed a few more games that are free to play on Steam that might be worth trying out. As such I thought I would collect them all together here for our reference. Tried Path of Exile
- ARPG, akin to Diablo 3 and Torchlight 2 Warframe
- A co-op FPS with RPG-like elements and ninja moves. Neverwinter
- An MMO based on D&D 4th edition. Alien Swarm
- 4 player squad-based top-down tactical shooter. Firefall
- A Borderlands-esque FPS MMO. Not Tried No More Room in Hell
- Looks to be a L4D/Killing Floor hybrid. War Thunder
- WWII based war MMO, looks a bit like the Battlefield games. Tribes: Ascend
- An FPS akin to the old Unreal Tournament games. Planetside 2
- An FPS MMO with large scale battles, vehicles and the like. Heros and Generals
- An FPS MMO based on WWII with online co-op campaign. Robocraft
- Looks to be a mix between Space Engineers / Kerbal Space Program where you make vehicles and fight them.
If you try out any, let us know what you think!