Manyland is an interesting 2D MMO where you can make your own vehicles, blocks, items, and characters using its sprite creator.

I think one of the most interesting things I've seen in that game was a group of floating Obama heads.

http://manyland.com/

It's also on iOS.

I love to play borderlands 2 with friends it is perfect game for blowing off steam.

Flappy Bird!

If you're on a phone, AA.

Best game to relieve stress or take a break from studies is always Graal. Just sitting down watching Guild sparring matches go on makes me feel too excited to wanna tag in and I get to chat/catch up with friends/people while I'm are online. Then there's Clash of Clans and Brave Frontier. App games keep me stress free while pc /ps3games just requires too much work to even call it a stress reliever.

Osu!