Garage Band is a Macintosh application that's in the iLife package of products (it may just come in the OS install, but I'm not sure.
I just downloaded a bunch more content and I'm really surprised, it goes into 12 bar blues, classic riffs, etc.
Took me all night, but I think I've got the intro to Roxanne (Stings' a great teacher
), now on to the next lesson.
Downloading does take forever as some of the lessons are bigger than 1.5 G