Twitter announcement: https://twitter.com/plan9foundation/status/13743504723168174...
Plan 9 Foundation: https://p9f.org/
Wikipedia: https://en.wikipedia.org/wiki/Plan_9_from_Bell_Labs
There's still a pretty active community around Plan 9, too.
9Front, a popular fork of Plan 9: http://9front.org/
Interviews with some Plan 9 community members: https://0intro.dev/
Some videos: [A Tour of Acme](https://www.youtube.com/watch?v=dP1xVpMPn8M), [Peertube channel of sigrid's](https://diode.zone/video-channels/necrocheesecake/videos)