After about a 15 year interlude I've started to look into doing pro audio on Linux again (I mean at a much deeper level than simple multi-tracking on Audacity). It was a bit too fiddly to seriously consider this back in 2005-2006 because we needed to build realtime kernels and hand-crafted drivers for professional sound cards and the entire system was quite unstable.
Anyway I've pulled a bunch of tools together and am impressed how they've all evolved. Still evaluating MIDI sequencers but to properly evaluate them I'll need to order a MIDI/USB cable to use my existing keyboard - without dragging in the entire rat's nest of MIDI gear in from the workshop. These adapters didn't exist back in the day, and my 8x8 MIDI interface is integrated into an audio rack with a bunch of dedicated automation and performance gear out in the workshop/shed.
This would be a bit much to try and cram into a limited office space and I really don't wish to work outside in winter. Eventually I might be able to link the two setups over wireless - but that's a task for another day.
I used to like rosegarden for sequencing but am currently leaning towards Ardour because it has video sync support. There's also LMMS but that seems to be designed more for loop production than multi-tracking audio/midi. Please let me know if you're aware of something better that I haven't yet discovered.