Music Related Free and Open Source Software?

An anonymous reader asks: "I'm going to a demonstration of some music software products tomorrow night. The music store hosting the event may be attempting to start a users group of music software. This seems like a job for open source advocacy! Anyone know of any good F/OSS for working with music and audio? I am already aware of Audacity and (Free as in Beer) Jeskola Buzz, but what else is there in the realm of sequencers and audio manipulation?" We did another helpful article back in 2001, and another from last August. What musical creations have you put together with any of this software, and others we may have missed?