Andrew Plotkin (Zarf) writes about interactive fiction, Infocom's Zork, and the code and history of its interpreters.
HN links it for deep dives into Zork and Infocom source code, including the Visible Zorker and the write-up on Infocom interpreters.
The others don't seem to have the MIT license pullreq added, so they are not open source; the source code is merely available. The repos have a note:
"This collection is meant for education, discussion, and historical work, allowing researchers and students to study how code was made for these interactive fiction games and how the system dealt with input and processing. It is not considered to be under an open license."
This github repo has been up for some years now (this old blog post has some back story: https://blog.zarfhome.com/2019/04/all-of-infocoms-game-source-code ) -- AFAIK it's the source contents from an old hard drive image from back when Infocom was a company.
(I only checked hitchhikers and starcross, because github is giving a lot of error pages for these right now.)
If you're at all interested in digging through the Zork code yourself, you no longer need to know Z-machine assembly: the source code for most Infocom games was released/leaked a few years back, and is available here: https://github.com/historicalsource/
It's written in ZIL, which has a somewhat Lispy feel (for a bit of background, see another post by Plotkin here: http://blog.zarfhome.com/2019/04/what-is-zil-anyway.html). Infocom's own internal documentation for ZIL is here: https://archive.org/details/Learning_ZIL_Steven_Eric_Meretzky_1995.
In http://blog.zarfhome.com/2017/08/your-load-is-too-heavy-zork-deep-reading.html , Andrew Plotkin was pointing to an Inform 6 version of Zork by Allen Garvin ,
http://plover.net/~agarvin/zork1.txt derived from the original decompiled Z-machine code.
Re: the Visual Zorker visualisation, see Andrew Plotkin's associated blog post: https://blog.zarfhome.com/2025/01/the-visible-zorker
[ commentless HN discs: https://news.ycombinator.com/item?id=42769679 ]
This reminds me of when the Infocom folks moved from the functional MDL to the micro-friendly ZIL, while keeping much of the syntax of the former: http://blog.zarfhome.com/2019/04/what-is-zil-anyway.html
It does, at least Zork runs, see http://blog.zarfhome.com/2019/04/all-of-infocoms-game-source-code.html and https://github.com/Homebrew/homebrew-core/pull/38990