Another cool project I recently found is Quickshell.
A number of components for building shells using Qt Markup Language. I saw QML for the first time in 2011, and I didn't enjoy it, but today it looks very sane to me (and I understand it much better :D).
If I ever need to prototype a bar, notification center, application launcher or something similar I would go for that. At least will start with it.
Demos are pretty cute and impressive:





