RAYGAN  I have been using this program for quite a while and I don't know if I could even begin to GM GURPS without it. This program isn't perfect but it's the best of it's kind on any platform as far as I am aware. It makes character creation, probably the most complicated part of the GURPS system, fast, fun, and easy to understand. I waited on switching to 4th edition rules for nearly a year until this program was made ready for them, and now that the update is here I can say that it's really quite good. If you play GURPS, don't miss this program.  
(Version 3.0.0.25)