An open-source drum machine and MIDI sequencer that also uses AI technology to figure out melodies for the patterns you program.
Ninjam is software that lets multiple people jam together over the Net. music composition Everybody can hear everybody else so they can coordinate what they're doing, tweak the mix, and alter the dynamics. You can play whatever you want during the session - sing, accoustic, electronic, wind instruments, what have you - as long as you can get it into a computer. MIDI is not required. Cross platform - Windows, OSX, and Linux. Clients connect to a Ninjam server that can be set up just about anywhere.
Software for composing music on a Linux box. Seems to have a tracker like interface. MIDI enabled. Seems to have a synthesis feature in addition to using samples. Can consolidate sequences into single objects. Embedded emulation of some of the greats, from the 303 and 803 to the 6581.
An online web app that you can use to generate and download blank staff paper for scoring music.