Oh! Lots of source. Good find! Big discussion here:
(And  this seems to be the announcement on twitter)
Related (I think):
“This is the source code for Zeugma (BBC Micro version), a modern Z-machine interpreter for the 6502 processor family.”
Edit: Nice pair of articles about Infocom’s Hitchhiker’s Guide in Jimmy Maher’s histories:
And for those wanting a little Jason Scott in their Infocom:
Actually, and I may well be misremembering here, a friend of mine had an opportunity to get archive back in the day. INFOCOM had effectively abandoned a Sun workstation that had all of this information on it. I think it was when they were shutting down, and they simply left it behind in the office space they weren’t using any more.
I appreciate the nostalgia, but was never a fan of the medium myself.
A couple of related links from some toots on mastodon (which will be terribly difficult to find later):
“ZILF is a set of tools for working with ZIL (the Zork Implementation Language), including a ZIL compiler, ZAP assembler, and ZIL libraries for writing text adventure games.”