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.