I found this site today on news.ycombinator.com/new, I think you guys might be interested in this
It's an overview of GUI's from various operating systems.
The site itself is also fun to browse through for a bit, its personality is refreshing compared to most template websites nowadays..
In a similar vein, have you tried Oberon OS? Wirth has somehow made it into a windows executable, it's interesting to play around with for a bit.