your options are Remeres Map Editor and SimOne's map editor, but Remere's is much better, and you can find it here:
hjnilsson/rme (https://github.com/hjnilsson/rme/releases)
note that Yurots-based 7.6 engines needs a small patch to make depots work with Remere's map editor, and Yurots was also the most popular engine of the era (most 7.6 distros are based on a Yurots engine, which itself was based on a OTServ CVS pre-release of 0.5.0)
(it's a minor patch but i don't remember it off the top of my head - if anyone is interested in that patch, let me know and i'll find it)