Frinika
Frinika is a free (licensed under GNU GPL) complete music workstation software containing sequencer, midi support, soft synthesizers, audio recorder, piano roll/tracker/notation editing and more. The goal of Frinika is to be a complete platform for making music with your computer, using the versatile Java platform to be able to run on several operating systems, and being open source to be able to embrace the best open source technology being available at any time.