https://www.pcgamer.com/a-coder-spent-1200-hours-reverse-engineering-diablos-source-code/

A coder who goes by the name of GalaxyHaxz has uploaded a reverse-engineered version of the original Diablo source code. According to this GitHub post, it took them over 1,200 hours over the course of "6-12 months", in bid to ensure "that everything is preserved."

Devilution, as the project is known, doesn't contain any of the original game's assets so don't expect a free copy of the classic action slasher. Do however expect an accessible project that aims to make things "much easier" to support and maintain into the future.