Ludwig is described as 'The music software Ludwig automatically arranges your songs with a few clicks. Accompanying parts fit the melody well. Automatic Chords. Pop, Rock, Jazz, Country, Classic' and is a Music Production App in the Audio & Music category. There are six alternatives to Ludwig for Windows, Mac and Linux. The best alternative is Impro-Visor, which is both free and Open Source. Other great apps like Ludwig are Band-in-a-Box (Paid), ChordPulse (Freemium), MMA (Free, Open Source) and Busker (Paid).
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.
Band-in-a-Box is an intelligent automatic accompaniment program. You can hear and play along to many song ideas and go from "nothing" to "something" in a very short period of time with Band-in-a-Box as your "on demand" backup band.
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.
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.