Qsynth - Qsynth is a simple Qt4 application wrapper for the ...
MuseScore.org - Create, play back and print beautiful sheet music with free and easy to use music notation software MuseScore. For Windows, Mac and Linux.
VirtualMIDISynth - VirtualMIDISynth is a software MIDI synthesizer implemented as a Windows multimedia user driver...
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ZynAddSubFX - ZynAddSubFX is an open source software synthesizer for Linux, Mac OS X and Microsoft Windows.
Finale - Finale, the world standard for music notation software, lets you compose, arrange, notate, and print engraver-quality sheet music.