"Music creation software" is a very broad category, actually. I'm guessing you mean a Digital Audio Workstation (DAW) where you can record sounds and instruments using some type of capture device through an audio interface.
I think Reaper is an excellent DAW. It has pretty good community support, and while technically the free download is only - legally - a 60-day trial, you can basically use the software's full functionality forever even when the trial license is expired. Even then, a license is only $60 for personal use.
Download it here:
http://www.reaper.fm/purchase.php