GNUstep

Preferred license: GNU Library or Lesser General Public License (LGPL)
GNUstep is a cross-platform, object-oriented framework for desktop application development. Based on the OpenStep specification originally created by NeXT (now Apple), GNUstep enables developers to rapidly build sophisticated software by employing a large library of reusable software components.
 
Current Projects
by Christopher Farber, mentored by Nicola Pero
by Christopher Elsmore, mentored by David Chisnall