Earlier this week, I had great success writing an avrdude clone (It is called AVRChick in the Chrome Store). This was cool, it flashes Arduinos with hex files over USB serial, but it didn't solve the problem: I want to write Arduino sketches on my reasonably powerful $150 laptop. It also runs on any computer with a Chrome browser with zero install. Thats nice too.
So here it is: the first version of an Arduino compatible IDE that can compile and upload your sketches over USB to your Arduino (most likely an Arduino Uno or 328 based board). It also has a terminal.
Chromeduino can be found here: https://chrome.google.com/webstore/detail/chromeduino/dmkincdpchiadkhhocmbpjljebfifgbl
I will be honest here. This is a major undertaking and the implementation is limited. It will take a bit of time to catch up. There is no library support and you can't do includes, and a few other minor things...but this should only be a few updates away.