Kongregate is a hub of gamers and gaming online. It includes some brilliant ideas that differentiate it from other gaming websites: it allows you to gain levels by accumulating points! To accumulate points, you have to be active in the Kongregate community, either by playing games and completing achievements, rating games, developing and uploading games or reviewing games. It's a ton of fun and there are thousands (literally) of free flash games rounded on this site. Hours of fun when you have nothing better to do :)
Some of the game achievements allow you to win certain cards. These collectible cards can then be played in Kongregate's original card game. It's actually quite a clever idea.
Also, there are contests every month for game developers to upload their new games. The game with the highest rating for the month gets some small cash prize ($1500 for October).
A few of my favorites include:
This cute tower defense game allows you to place balloon popping towers and pop your heart out! Watch out for those MOABs! (Mother Of All Boats). You'll love to hate balloons.
Clever idea for a puzzle game. There are two worlds that you can "shift" through, one black, one white, each one is a reverse of the other, including gravity. You have to find out how to get to the exit without dying by shifting through the two sides. Plenty of fun, and quirky storyline reminiscent of The Orange Box's "Portal".
(From Guy Du Blag.)