Oh so cool! Do you know of other themes like it, also open source?

This is close: https://panr.github.io/hugo-theme-terminal-demo/

Unfortunately not, I've just had this one opened in my browser for ages as a reminder (after seeing it on HN IIRC) and recognised it again in the OP instantly :)

I've never heard of it and I already like it.

yes! great theme