After more than four years work (Sourceforge registration date) the project is now at 0.8.4. And it’s not only doing the GUI part wxWidgets (C++); it’s also doing DBs and Files and ZIPs. wxWidgets means more than just GUI APIs – there’s other stuff available such networking, config file managers and logging – all to help you to write cross platform GUIs in C++.
wxJS also provides XML support (OK Expat not libxml2 but anyway) and Spidermonkey’s E4X support is apparently enabled.
Not that I’ve tried wxJS yet but fascinating stuff ;) Right now Windows only binaries but looks buildable on Linux.