If you're into music composition, Rosegarden may be of interest. It's a MIDI sequencer and notation editor, which also has basic audio capabilities (recording and playback). Connecting with Jack, LADSPA and DSSI plugins, featuring a powerful notation editor, Rosegarden should fit nicely into your home studio. If classical notation doesn't fit your needs it also offers a "piano roll" editor along with a percussion editor. The next version should feature lots of improvement in notation handling, along with other modes like guitar tablature for instance.