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!
Oh forgot to mention, the GoG release runs on Windows 7+ while the original release from Internet Archive I think you need to download DGVoodoo 2 or another wrapper to play on a modern os. Honestly it's easier just to dl the original game, copy the files, and play the source port Devilution X.