A very nice Scheme programming environment whose main goal is learning programming itself - building on Scheme language scopes of varying complexity. The whole thing is well-oriented to what is necessary at each respective level. In addition, a large collection of libraries with useful function definitions, a graphical programming environment, and a corresponding library for your own programs, many useful developer tools (and some optionally installable developer tools that you can't get elsewhere), and the best part: now also runs on OS X. Nice.