Its operating system demo (from Computerphile)

This famous 'hacker OS' was the birthplace of rather a lot - emacs, AI living in a 3D world, as well as the Open Source culture. A reconstruction project has brought it back to life. It's fun to experience what it was like circa 1973, having a heavyweight PDP-10 mainframe class machine hacked on for fun and exploration.

The software used in the Computerphile episode can run on any Pi - and, in fact, any Linux - without the replica hardware.

I hope this gets some attention to an OS right at the root of what we're living with day to day now!