one of the most useful apps for the jazz musician is iReal Pro. it is a go-to app for gigs and for the practice room. i use it to warm-up and to learn songs. check out their site for demos and to download the app. it may be one of the most expensive apps out there, but it’s worth every cent. HIGHLY RECOMMENDED.

along those lines…

for students just learning the language and sound of jazz, sometimes the etudes “don’t sound right” to the ear. using the play-along track will help give your ear the right context of harmony and bass line, speeding up your aural understanding of the way the etudes “really sound.”