It's powered by Awesomium, which is basically Google Chrome wrapped up in to a standalone app. It's free for indie developers providing you made less than $100k last year, after which there's a fee (which is small compared to your revenue if you just made $100k).
Some parts of it are very cool:
- Renders with WebGL
- Supports Web Audio API for reliable polyphonic low-latency audio
- Completely self-contained - includes all the necessary files in the download and works offline
- It should be possible to access files on disk as well.
There are some minor disadvantages:
- Since Chrome is a complete commercial-quality browser engine, it adds about 15mb to the zipped download size. There's not much that can be done to avoid it. I suppose you're more likely to be targeting larger games for the desktop, so hopefully that size isn't so big when taking in to account all the assets of your game.
- Currently the demo will chew up more CPU than it needs and run slower than it would normally in the Chrome browser. We know why this is and we're trying to help Awesomium to fix it.
- If your computer does not support WebGL it will fall back to a slower canvas 2D. We also know why this is and we can get WebGL enabled for all computers, which is better than the browser itself, and we're also trying to help Awesomium get that sorted too.
Anyway, experimental support should be coming in the next beta release in a few days!