wxWidgets based WM/DE
is there an entire window manager / desktop environment that only uses wxwidgets?
Not currently that I know of- since WX is more of a wrapper around GDI, GTK+, and Carbon on their respective platforms, I'm not surprised that this is the case. All WX brings to the table is a clean way to make apps for multiple platforms, so it's a little less useful to make a window manager or desktop environment as it's an unneeded (for that sort of application) abstraction layer.
Ayup! Think of it as a higher level abstraction layer to individual "low level" APIs for GUIs.