A telescope with a liquid mirror.
(Science Week, day 3!)
The basic idea for a liquid mirror telescope is to use a thin layer of mercury, then spin it slowly. The rotation of the frame causes the liquid to form a parabolic surface. Combined with secondary mirrors or lenses, you then have a working telescope.
This comes from the beautiful site of Brian Koberlein, along with an image of one that actually operated from 2003 to 2016. I imagine the name "Large Zenith Telescope" owed to the reluctance of flat liquid surfaces to… you know, tilt.
But Brian elaborates on the possibility of actually using liquid telescopes that do tilt!