My original plan is to build a minimalist Common Lisp GUI library over some 3d engine. Right now, I'm wavering between raw OpenGL and a full- fledged game engine, probably from the C world.
Like everything else in life, both approaches have their tradeoffs.
Right now I'm leaning toward rolling my own over the lowest-level layer I can get my hands on. Right now, like frereth (which will most likely be built on top of this...or maybe atop a more full-featured widget set that sits in between), this is pretty much complete and total vaporware.
I'm really just getting a feel for the various tools that I think I'll most likely be using. Making the project public just means it's more likely I'll actually do something with it.