Use Adobe AIR runtime and program in js. But no, if I'm using AIR, the AS3 suites it the most. So not a good option.
GWT: No because it uses Java and then convert it to js or what ever.
The documentation may be a bit weak in some areas, but it's a solid platform for developing.
Maybe Mozilla Prism is what you are looking for?
Prism is an application that lets users split web applications out of their browser and run them directly on their desktop.