Its called iReal b
Not only does it play back chords from some of your favorite jazz standards so you can practice your licks and improvisation, you can:
1. Transpose on the fly
2. Display chord names OR chord numbers (I, V7, VI, etc)
3. Edit individual chord voicing in a tune
4. Alter playback (for instance, you can have the song play through once at regular tempo, then play again at a faster or slower tempo and in a different key)
5. Display chord voicings AND right hand piano voicings in real time
6. Create and upload your own songs in the editor
7. Output songs as wav files
8. Adjust volume for each instrument (drums, keys/guitar, bass), you can even solo each instrument (for instance, you can solo everything but the bass to get a feel for what your bassline might work)
9. Change play style (you can have a song played in a jazz feel, or rock feel, or pop feel)
10. Expand your musical vocabulary and perhaps learn new chord arrangements for use in your own compositions
My piano instructor put me on to this last night and after playing around with it, I love it! Its easy to use and great for practicing chord changes and ear training as well. They have an active forum where you can download user made tunes for free. The software costs $8, but its worth the price, believe me.
For you frustrated, impatient, "too-lazy-to-learn" beatmakers, I know it sucks when you ask Bandcoach to give you the chords to a song and you don't understand his answer (LMAO). With iReal B, you can plug in the chords he gives you into the editor and play 'em back for yourself. This should be in EVERY producer's arsenal. Sleep if you want to, or get in the game.