Band2play is a free program that converts chords, eg: (Am, D7, B7b9) to a MIDI playback file. It´s a very simple program with a powerful conversion engine programmed by Christoph Schröder. You can chose a lot of different backing styles, like Jazz, Latin Jazz, Pop, ...

You may use it as a generator for play-a-longs for jazz standards and improvisation, for singing, for generating any playback you want. You just need the chords.