Diablo is a classic and it can live on forever thanks to open source. Freeablo is a cross-platform free and open source game engine and it just had a massive update.
Not to be confused with Devilution and devilutionX, which are reverse engineered and walk a pretty iffy legal line. Freeablo, instead, is an original GPL licensed re-implementation for getting Diablo running on modern platforms. Think of it like OpenMW for Morrowind and openXcom for X-COM.
What's new in Freeablo v0.4? A huge amount including: multiplayer, save/load, monster attack animations, melee combat, town NPCs, a dialogue system, player inventory and much much more—it's getting into a much more playable state. Check out the release trailer for Freeablo 0.4:
It needs the original data files like other open source re-implementations, you can pick up a copy of Diablo from GOG.com for that. This release actually adds support for the GOG version too!
Hat tip to Lightkey.