The game ikaris (
ikaris.net) is a 3rd person shooter / sidescroller, it is in-browser and exclusively multiplayer, which means no download or registration is required, you can jump straight into a game in seconds. And, it is now in beta, looking for a community to help develop further what already seems like a pretty neat game.
To join a game you can go to
ikaris.net/joinOr, to jump straight into a random game go to
http://www.ikaris.net/node/15?gameID=random and enter a handle to begin.
Here is a screenshot: The more players there are, the more fun it is, so drag a few friends in. I'll see you in the game!