Is this not more intended for guitars? It talks about chords and backing tracks. I had a quick look but I'm not sure how it relates to Saxophones. The other good site for free stuff is http://www.8notes.com/
If you have an Android device try... http://www.irealb.com/android/that looks like a really good app - might be worth getting an iphone for!!!
If you mean they are just backing tracks playing just percussion and chords they sound perfect for playing sax over either with the head (melody) or improvisations. (And one day I'll be able to do it!)