So, there are projects like these;

www.dfworkshop.net

vcmi.eu

github.com/ihhub/fheroes2

zdoom.org/index

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)