Ludwig!

Impro-Visor (short for “Improvisation Advisor”) is a music notation program designed to help jazz musicians compose and hear solos similar to ones that might be improvised. The objective is to improve understanding of solo construction and tune chord changes. There are other, secondary, things it can do, such as improvise on its own. It has also been used for transcription. Because rhythm-section (e.g. piano, bass, drums) accompaniment is automatically generated from chords, Impro-Visor can be used as a play-along device. Now having a wider array of accompaniment styles, its use is not limited to jazz. »

ChordPulse is a handy backing band software for music practice, inspiration, improvisation, and pure fun with music. Play and sing along with ChordPulse. Use it as a full accompaniment, a drum machine with bass, a metronome with chords, and more.

Band-in-a-Box is so easy to use! Just type in the chords for any song using standard chord symbols (like C, Fm7, or C13b9), choose the style you'd like, and Band-in-a-Box does the rest... Band-in-a-Box automatically generates a complete professional-quality arrangement of piano, bass, drums, guitar, and strings or horns.

“MMA—Musical MIDI Accompaniment” is an accompaniment generator. It creates MIDI tracks for a soloist to perform over from a user supplied file containing chords and MMA directives.

Busker is a complete set of tools to create musical arrangements from sheet music (chords + melody staff). It uses Yamaha compatible styles (thousands can be downloaded for free) for auto-accompaniment. Once you entered the song you can easily play it with many different styles and try different multivoices with auto-harmonies.