iReal App/Program
The first program to be adopted as a learning and backing tool by the music community was Band In A Box. The newest tool to become widely adopted is iReal (http://www.irealb.com). For our blues harmonica world, jam tracks are superior due to their high quality, but where they fall short is in the ability to make custom chord changes for those wishing to study non-12 bar blues or chords in their raw form (music theory study), where the backing doesn't need to be inspiring... it just needs to be what you need it to be.
If you're studying Music Theory Study 6 or Accompaniment Studies 3/5, having iReal can be very handy.
In Theory Study 6 we dig into non-12 bar blues chord changes. You can input the same chords that I provide in the PDF to iReal... choose a tempo, a key, and away you go... for as long as you need to... to get your playing dialed in to match those unfamiliar chords. The loop function is worth its price in gold... you can work on just a small, troublesome passage until you have it. Once you're done creating your charts you can save it as a music file to use in your music player (though working with the chart within the program is superior).
The same idea works well for your accompaniment studies. Write out a basic 12 bar blues, choose a feel, tempo and key and go to work dialing in each hole (the Hole Changes concept). Many find looping the last four bars very helpful due to its fast harmonic pacing.
Another fun tool of the digital age for an age-old art form.