Actually, yeah. It's not much, but ZDooM (UZDooM) is a very fun little game engine to scratch that 90s FPS itch, with its own scripting language for new content. I have a very broken mod in the works (wow, has it been a year...?)
It's still not yet ready to advertise, but Patreon patrons are getting a kick out of the prototype in early access. At least so far...