Just because it hasn't been mentioned in this track, there also is qtractor. And there's the non tool suite. I've only played a bit with both, so I can't say a lot about them.
qtractor is the best thing I've seen on linux. (MIDI user for > 20 years.) It continues to be actively developed; The latest version is 0.9.0.
( If you need to use audio, though, that's a harder question.)