Inferno OS source code was released under open source license
bitbucket.org
bitbucket.org
https://github.com/leimy/9ferno-leimy
It's based on the 9ferno repo hosted with the 9front project (Plan 9 fork)
http://git.9front.org/plan9front/9ferno/HEAD/info.html
I've not gotten Apple Silicon support working, but that would certainly be welcome. This is amd64 only.
(Not sure if Joe has taken my changes into his branch yet, but they might be there.)
edit: MIT, I think. I'm not used to bitbucket and was browsing the files, but it was more easily found via commits.
https://bitbucket.org/inferno-os/inferno-os/commits/6cde411a...
I also am used to LICENSE or COPYING, but I think they're calling the files NOTICE.