it's chromium embedded framework[1]. it's technically a c++ application. in theory very close to how brackets works[2]. but they use the chrome rendering engine for text storage and all the drawing, which in theory means that it's easier to port across osx/windows/linux. there's still some platform specific code in there.

think about it a little like xulrunner

[1]: https://code.google.com/p/chromiumembedded/

[2]: http://brackets.io