GNUstep Renaissance allows you to describe your user interfaces (that is, the windows in your application, and the buttons, boxes, textfields, etc in the windows) in simple and intuitive XML files, using an open, standard format describing the logic of the interface. GNUstep Renaissance can then, at run time, generate the user interfaces (using the native host OpenStep-like libraries) by reading the XML files.
WWW: http://www.gnustep.it/Renaissance/