So, there are projects like these;
https://github.com/ihhub/fheroes2
Projects that in one way or another aim to modernize a classic, or try make it more playable on modern machine, or just try to expand on things (like gzdoom does)
what other projects are out there in a similar vein?
I find this a little difficult to search for, even with specific terms (i tried finding myself)
There’s loads of source ports and game engine recreations. I think if you search for “source port” you can find most. For example
Ship of Harkinian an Ocarina of Time port
SpaceCadetPinball from windows 9x/xp
Rigel Engine for a native higher res Duke nukem 2.
Lemmini a Lemmings port
DXX Retro a descent 1/2 port
RVGL a re-volt port
Among others.