I know there was the thread here, ages ago, about the infocom games and their source code written in their own format.
Looking at an abandoned software site, I found this gem...
https://vetusware.com/download/Windows%20Frotz%201.15/?id=7251
it's the interpreter that reads the game data to play the games.
"Windows Frotz is an interpreter that can play all the old Infocom text adventures. Infocom used a clever system to write their games: they had a system that produced a data file for the adventure that was the same on every computer, and an interpreter for every computer that could run all the games (It was actually a bit more complicated than that, but that's the basic idea)."
I've already downloaded the 2 files I can for today, Heretic being one, so I can't download anything else till tomorrow, so I can't verify its claims.

There are multiple interpreters for Z-machine out there. There's some mac ones too. If you're going to download WinFrotz I'd recommend just getting it from their github page. The version on that abandonware site is ten years out of date at least and the source is questionable.

Thanks for letting me know.

Also have a look here The Interactive Fiction Archive and frotz interpreters are shown here