Gorm (Graphic Object Relationship Modeller) is a GNUstep application for building user interfaces and application objects relationships. Its major features include drag-and-drop creation of GUI elements from palettes, run-time loading of additional palettes, direct on-screen manipulation of GUI elements, manipulation and examination of objects via inspectors, and creation of connections between objects using mouse. It is a clone of the former NeXTstep (currently OS X) "Interface Builder" application.
Setedit is a text editor specially designed for programmers. It has a nice interface with mouse support, menus and windows (text mode). The editor is a very good choice for people with DOS background, especially people accustomed to Worstar and Borland editors. The editor has overlapped windows so you can see more than one file at the same time, configurable syntax highlighting, macros, rectangular selection, block indentation, as well as customizable keyboard shortcuts and menus.
Squeak is an OpenSource and super-portable implementation of a multi-media capable Smalltalk-80 based object-oriented programming environment. It is written entirely in Smalltalk and has a high-performance VM, created by compiling the Smalltalk VM code into efficient and portable C code. It now uses the Self language's Morphic User Interface but still provides the original MVC GUI as well.