Microsoft Songsmith is described as 'Songsmith generates musical accompaniment to match a singer’s voice. Just choose a musical style, sing into your PC’s microphone, and Songsmith will create backing music for you' and is an app in the Audio & Music category. There are more than 10 alternatives to Microsoft Songsmith for Windows, Mac, Linux, iPhone and iPad. The best alternative is Impro-Visor, which is both free and Open Source. Other great apps like Microsoft Songsmith are Band-in-a-Box (Paid), ChordPulse (Freemium), Chord Pad (Paid) and MMA (Free, Open Source).
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.
Described as chord sequencer it lets you quickly create chord progressions, play them in many styles, transpose, adjust tempo, change instruments. Great for practicing. I used it for improving my scales on guitar and I have to tell it is amazing.
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.
Groovyband Live! is a realtime arranger software that runs on any Windows PC (tablet, laptop, desktop), interfaces with MIDI input devices (keyboards, pedal board, control surfaces) and produces a live stream of MIDI events to drive a suitable sound generator.