One domain that a little OO seems to map to without too much pain is GUI libraries. The first OO-flavoured API I ever used was Sunview, the early GUI I used on Sun-3 workstations with SunOS. It was a beautiful API; I was never tempted to mess with the verbose, complex "Intrinsics-based" toolkits that followed it. It carried on with xview; that's what I'd try if I wanted to write a GUI in C today.
