MuseScore is a free music notation and composition software available for Windows, Mac, and Linux.
OpenMPT (short hand for Open ModPlug Tracker) is a popular tracker software for Windows. OpenMPT is completely free and allows you to create and play back some great music on your computer. Based on the original ModPlug Tracker written by Olivier Lapicque, OpenMPT is free...
Sibelius is a scorewriter program, created by Sibelius Software (now part of Avid Technology) for Microsoft Windows, OS X, and historically RISC OS.
GNU LilyPond is a computer program for music engraving. One of LilyPonds major goals is to produce scores that are engraved with traditional layout rules, reflecting the era when scores were engraved by hand.
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.
GNU Denemo is a music notation editor that lets you rapidly enter notation for typesetting via the LilyPond music engraver. You can compose, transcribe, arrange, listen to the music and much 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.