This is something I have seen. I have used ZZT, and it is still used even now. One of my ZZT games includes a note that although the world itself is Free software, it is "trapped" because ZZT isn't. That was written before ZZT source code has been reconstructed in this way, and now ZZT is Free software, although it is itself "trapped" because the compiler isn't. There are many tricks and stuff involved in ZZT and I have figured out some things just by trying and then make the hypothesis how they worked, and now I can check the source code to see if it matches what I expected, too. But I can see in there also many things I did not know ZZT does, so this is helpful. Other people have also independently figured out many kind of tricks with ZZT (see [0] and [1] for some details). I also wrote my own external editor for ZZT (although unfortunately it is slow, and confusing, but I like it, and prefer that kind of user interface, which is why I wrote it, of course).
There are now other ZZT-likes, the most popular of which is probably MegaZeux (which is now Free software, and continues to be maintained), although there is also ZIG, and a few others, including my own ZZ Zero. Each of them has different set of features. Although, most of them aren't used much other than ZZT and MegaZeux, I think.
The GitHub mentions to fix 5 annoying bugs in ZZT. I thought of fixing some bugs in ZZT (although not those that affect the behaviour of the game), and removing the editor (you can use an external editor instead, such as KevEdit or ZZTQED) and any stuff that is in there because it is only used by the editor, and probably also removing mouse and joystick mode and monochrome mode and VideoWriteTextCO40 (I don't know why that is in there, since ZZT doesn't use the forty column mode), and removing the initial prompt (to make it faster to load and further reduce the file size), and possibly adding an additional optional header in the world file which controls some new features and bug fixes, and allows customizing the contents of the ElementDefs array (the first number in the file would be different, so you can tell apart from standard ZZT worlds). I don't know when or if I might try to do this, though; I will of course need to install Turbo Pascal first, and read its documentation, before I could do such a thing.
There are now other ZZT-likes, the most popular of which is probably MegaZeux (which is now Free software, and continues to be maintained), although there is also ZIG, and a few others, including my own ZZ Zero. Each of them has different set of features. Although, most of them aren't used much other than ZZT and MegaZeux, I think.
The GitHub mentions to fix 5 annoying bugs in ZZT. I thought of fixing some bugs in ZZT (although not those that affect the behaviour of the game), and removing the editor (you can use an external editor instead, such as KevEdit or ZZTQED) and any stuff that is in there because it is only used by the editor, and probably also removing mouse and joystick mode and monochrome mode and VideoWriteTextCO40 (I don't know why that is in there, since ZZT doesn't use the forty column mode), and removing the initial prompt (to make it faster to load and further reduce the file size), and possibly adding an additional optional header in the world file which controls some new features and bug fixes, and allows customizing the contents of the ElementDefs array (the first number in the file would be different, so you can tell apart from standard ZZT worlds). I don't know when or if I might try to do this, though; I will of course need to install Turbo Pascal first, and read its documentation, before I could do such a thing.
[0] https://rabbitboots.com/kfx/index.php/ZZT_Notes
[1] https://rabbitboots.com/kfx/index.php/ZZT_On_ZZT