Busker is described as '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'. There are more than 50 alternatives to Busker for a variety of platforms, including Windows, Mac, Linux, BSD and iPad. The best alternative is Rosegarden, which is both free and Open Source. Other great apps like Busker are Guitarix (Free, Open Source), Avid Sibelius (Freemium), Frescobaldi (Free, Open Source) and Power Tab Editor (Free).
Power Tab Editor is a free tablature authoring tool created by Brad Larsen for Windows. It is used to create guitar, bass and ukulele tablature scores, among many others. The current version uses the *.ptb file format.
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.
Aria Maestosa is an open-source (GPL) midi tracker/editor. It lets you compose, edit and play midi files with a few clicks in a user-friendly interface offering keyboard, guitar, drum and controller views.
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 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.