VisLua is a full featured IDE for the Lua scripting language written in Lua. VisLua supports full context debugging, syntax highlighing, and many other advanced IDE features.
vMac is a free Open Source Macintosh emulator that is available for Linux/X-Windows, Win32, DOS, MacOS, and more.
A cross-platform wxWindows class for running Ghostscript and manipulating the image it produces, plus an IDE/debugger for developing programs written in PostScript. For a PostScript debugger, there is now also an Eclipse plug-in - see http://thomas-fritsch.github.io/psdt/