I had another check to see if anyone else is making an open source RPG, and I can't find anything undernearth all the lies.
Open Legend takes 5000 words to explain that you can reference their SRD (i.e. make a bibliography), but nothing else:
https://openlegendrpg.com/community-license
Expedition has source code, but requires an 'app'. Unsure if this qualifies as a 'tabletop RPG'.