Perhaps a viable solution is to take an approach similar to wxWindows, and  
write a library the uses a native library on each major platform (e.g.  
GTK2 or QT3 on *nix, GDI on Windows, and Cocoa on Mac OS X. This way you  
get a native interface on each paltform, as well as saving the effort of  
having to actually write a low-level toolkit. That was programming effort  
could be spent solely on the actual API.

-- 
Tyler Eaves
<tylere@mailshack.com>