The Dark Mod is a fan-made spiritual successor to that style of gameplay, running on id Tech 4 (the engine of Doom 3) and carrying on its overall style very well - the engine lends itself to moody lighting and surprisingly sophisticated enemy AI, and while the physics are slightly clumsy, they capture the feel of classic Thief almost perfectly. Things are changed up a bit, though; the lockpicking is more of a timing-based minigame and there is no running storyline (unsurprising, as most of the levels are standalone fan-made missions). Still, fans of Thief's gameplay should have a lot to like here; there are dozens of fan-made missions available, and all of it is, of course, completely free.
Free Game Friday 9/13/19: The Dark Mod
Thief is an undeniable classic for the PC platform, meshing well-realized, objective-based stealth gameplay with dark fantasy elements and a consistently unsettling atmosphere to provide an amazing experience on every front. Basically, you were sneaking through a huge variety of locations (from haunted crypts to mage towers to castles to churches), discreetly knocking out guards so you could slip through, using clever gadgets like water arrows, rope arrows, flash bombs and gas mines, and stuffing anything valuable into your pockets for later use while staying one step ahead of monster and guard alike. In short, it's one of the best games ever made.