Through reading up on Gloomwood, I also discovered "Filcher".. a much more minimalist Thief-alike, but also much closer to the spirit and mechanics of the original Thief.

Filcher takes place in a Noir Art-Deco 1920s, where the player robs socialites, mobsters, and company high-rises instead of Thief's noble manors and Hammer temples.

It adds a few modern-day tools (like a flashlight and a tranq dart gun), and it lacks voice acting, but aside from that it's the closest one can get to a new Thief game without actually being one.

http://filchergame.com/