If you want to have Jam sessions, blues is the most important basic chord progression.
This application helps you to practice scales that could be used in blues.
Practice scales and make your own bluesy melodies!!
Also it provides famous jazz blues standards and over 150 licks to help you to get bluesy ideas.
This application also provides Piano & Guitar comping/voicing, Bass line and Drum beats for each genre such as Swing, Funky, R&B, Rock, Shuffle and Latin.
You can adjust each instruments volume at the Mixer.
Also, try Jazz Scale if you want to practice more chords and scales!
Http://itun.es/iBY3jY