I just read about Factor on Dave Roberts' Finding Lisp blog. While I don't expect to do anything serious with Factor, I must say: it is very well done - at least the Mac OS X version that I tried. Add creative to well done. Read what Dave has to say about Factor (he also has good things to say about Erlang, for which I have been investing some learning time in the last month) and install Factor to see an interesting light weight environment. Factor reminds me slightly of using Oberon (a long time ago): a different way to work.