Band-in-a-Box 2013 for Mac
Band in a Box is a terrific tool on a lot of levels. I use it for a couple of reasons. 1) For myself as a way to practice new tunes with a rhythm section, Being able to vary tempos really helps in getting a tune under your fingers. I also use it to compose my own songs. I can hear how I might want to voice chords to get the best results.
2) For making my students a practice disc of material that we're working on.
PG Music has added a lot of new features from an older version which I used to use. I'm finding that it takes a bit of time to get used to. In a way, these features are a bit overwhelming, and require some patience to learn. However, overall it's a great device for self improvement.