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It's almost disgusting how easy it is to write fairly complex programs under Cocoa/OpenStep. Objective-C combined with powerful foundation classes is really only a small step up in difficulty from "light" programming languages such as VB, PHP, or Perl. I'm working on some innovative software right now that I plan to release for OS X by the end of the year, and it's only possible because of Cocoa. Perhaps I'll start working on a port to GNUstep as well.