I am a professional musician. For getting things typeset, I use Lilypond, and the two tools I use are vim and rumor. (https://launchpad.net/rumor) Very simple, but it gets the job done.
For live performance, I have a USB keyboard and several voices in Csound (http://www.csounds.com/) and run the whole thing through a keyboard amp. Cheap and effective.
Thank you for comment. Did not hear about rumor before. I'll have to definitely check this out, even though it's not suited for prototyping. I'll test Csound too.
For live performance, I have a USB keyboard and several voices in Csound (http://www.csounds.com/) and run the whole thing through a keyboard amp. Cheap and effective.