It's also on GoG https://gog-games.to/game/diablo and Internet Archive https://archive.org/details/Diablo_1996_Blizzard

To play the source port all you need to do is copy some files from the retail into the folder and it's good to go. It's also got quality of life changes like monster health bars, widescreen support, and a stash that transfers across characters. There's also multiplayer for classic and hellfire!