Here are some links I found as I listened to the episode.  Tried to get them as I listened since I forgot to send them to Pat due to the holidays.

This page has been around for years.  Some links might be stale or dead.
https://linux-sound.org/

Some of the sound fonts I've used:
https://midkar.com/soundfonts/
https://www.pvv.org/~hammer
https://www.michaelpichermusic.com/sample-libraries

MIDI/Music software discussed:
JACK (JACK Audio Connection Kit)
https://jackaudio.org/
Qtractor
https://qtractor.sourceforge.io/
Ardour
https://ardour.org/
Reaper
https://www.reaper.fm/index.php
Carla
https://kx.studio/Applications:Carla
Duality Bass 
https://audio-assault.com/duality.php

My Soundcloud page.
https://www.soundcloud.com/claudiom72

Open source synthesizers:
https://www.moddevices.com/
https://www.linuxsynths.com/
https://en.wikipedia.org/wiki/Korg_OASYS (Finally found that hardware Linux-based synth.)
https://synthesia.sourceforge.net/
https://zynthian.org/ (Don't remember if this was mentioned, but here it is. :-p)

Pipewire
https://pipewire.org/

unfa
https://www.youtube.com/channel/UCAYKj_peyESIMDp5LtHlH2A