What are some great free multiplayer games? (PC)

So I have a simple question, what are some great multiplayer games? I'm looking for some online games I can easily set up and play with friends.

I would prefer to avoid games like League of Legends that would require getting a installer and launching it. But if an amazing game like that comes to mind, feel free to mention it!

Any suggestions are appreciated!

EDIT: I should have probably added that I'm looking for PC games.

Is it bad I like World of Tanks? Also Hawken is good. And of course there is LoL and Dota 2. Super Monday Night Combat and Ghost Recon Online too. All of which have installers.

Super Monday Night Combat is pretty good. As well as Good ol' Team Fortress 2.

Gotham City Imposters is a fun one that most people forgot, I've been playing way too much Warframe at the moment which is probably the one free multiplayer game I'd recommend.

Planetside 2 is pretty fun

Dota 2!

Does Soldat still work? Goddam that game is amazing.

League of Legends is the F2P multiplayer game at the moment, though if you don't want to fall down the MOBA hole (and I wouldn't blame you), I imagine something in Steam's Free to Play section is worth a gander.

I really can't think of any game that doesn't need to be installed that's good. Most online browser games are kind of bad. I'll just say Warframe (It's on Steam). it's a very fun third person shooter.

Team fortress 2

Gotham City Impostors

Borderlands

Left 4 Dead 2

Dungeon Defenders

Edit: Didn't realize you said FREE games.

Team Fortress 2, Super Monday Night Combat, DotA 2 (I have a code if you want it), Warframe, Planetside 2 and if you want an MMORPG, I'd just advise you to get Guild Wars 2 instead of looking for a free one.

Thanks for the suggestions! I'll be looking at all those games. I guess any "good" games will have installers, which isn't necessarily bad.

Tribes Ascend! Everyone stop recommending all those other games and start recommending TRIIIIBES. But, seriously, Tribes Ascend is amazing and does Free to Play really well. You can happily play the full game, forever, and not spend a penny.

If I had to suggest other games, I'd go Team Fortress 2 (although you should know that it's a *big* download these days! So much added stuff) and Gotham City Imposters. GCI is very quick and CoD like. Pretty simple but loads of fun. Would be super fun with friends.

Mechwarrior Online?

Quake Live

Tera: Online

Be wary though, the questing is literally a traditional MMO to the core.

Combat is fun though!

Super Monday Night Combat, Blacklight: Retribution, Tribes Ascend, Planetside 2, Team Fortress 2, Star Wars The Old Republic, Tera: Online, League of Legends.

I agree completely. Tribes Ascend is a blast and they handle the free-to-play aspects really well. It's definitely the best free-to-play game I've ever played. I don't even like most multiplayer shooters, but Tribes is different enough from most shooters that it really hooked me.