Heya,
I recently came across a site of a programmer that made it able to play the first game of the C&C series on the browser. Even with campaign, multiplayer, music etc.! Which is quite the feat to be honest!
Admittedly the game is old so might not be interesting for anyone who does not have nostalgia but being able to play against your friends or anyone else online without registration or download is super cool. Guess it's just not very known so figured I might post it here incase anyone is interested in playing some!~
http://www.adityaravishankar.com/pro...d-and-conquer/
Just click multiplayer->join room and you're set.
If you want to find the page via google just search: command and conquer html5
Enjoy!