Long time ago, the Game Developer magazine published an article about ID Software and their DOOM game. In the article ID states that they used a NeXT Step machine for development with GNU GCC cross compiler. Quoting:
By writing in ANSI C on NeXTStep, Id Software is able to develop and test in a true programmer’s environment. Then, using a network, developers are able to send the code to a test PC running DOS and recompile what they are working on to run the game on its natural environment.
NextStep evolved into Cocoa, and other OSes have grown with other UI frameworks, GTK, Qt, MFC, etc...
Saying that one wants to get a "real development environment" has the OpenStep project evolved in a way that it can compete with Cocoa/MFC/GTK/Qt?
Judging only by the project screenshots it looks like the framework stopped in time, the widgets are not as nice as the ones from the other frameworks I've stated, but ugliness is not a software development measure, how is the support, maturity and completeness of OpenStep widgets?