Gom!
Gom allows you to write GTK applications using JavaScript and an HTML-like widget layout syntax.
It does this by first implementing a W3C DOM Level 1 (Core) API for interacting with GTK widgets and windows, then by providing a JavaScript binding to this layer.
Those are the goals, at any rate. It is certainly a work in progress; basically examples/hello.gom works and probably not much more.
Gom is on the Web!
http://ilovegom.googlecode.com/
To build Gom, you need to check out and build Mozilla's JavaScript engine - SpiderMonkey. Instructions are here:
http://developer.mozilla.org/en/docs/SpiderMonkey_Build_Documentation
Don't worry, it is a small amount of code and should build easily and quickly.
When running Gom's configure script, you should point it at your mozilla checkout using the --with-mozilla-source=<path> option.
Once you've build gom, you can pass a .gom file to load on the command line:
$ ./gom examples/hello.gom
It will spew a bunch of garbage to the command line, but if all goes well a window will pop up. Close the window with your windowmanager, and gom should exit.