Strife: Quest for the Sigil
The Steam link above points to the Veteran Edition, a port for modern systems with a number of changes and additions, including Steam achievements. I actually played the original Strife through GZDoom, which allowed me to run it on macOS.
Strife isn’t particularly well known, and I think it deserves far more recognition than it gets. I finished it several times back in my school days. It runs on the Doom engine, yet feels remarkably different from Doom itself. If I had to define its genre, I’d call it 3D action with RPG and stealth elements, set in a world that blends fantasy and cyberpunk.
For 1996, this combination was something genuinely new: character progression, an inventory system, NPCs, quests, an engaging story, and multiple endings.