There are two things fans like to port themselves. Games not made for Sega Genesis / Mega Drive to the Sega Genesis / Mega Drive and porting various Castlevania games.
Now fan developer werton is doing both by working on a port of the PC Engine classic Castlevania: Rondo of Blood / Akumajō Dracula X: Chi no Rondo, originally released back in 1993.
The conversion is being made “from scratch” and is being coded in C using SGDK.
You can see footage of the project below, which looks very promising, and seems to be a fairly close match to the original game.