Models of several early, and later discarded, space shuttle concepts.
The Harmon Kardon RABCO was one of the first (or maybe the first) commercially available linear tracking turntable. It was for its time a striking piece of industrial design and a lovely object in assembly, conception and quality of materials. It was beautiful, solidly built, and completely impractical to own.
Speaking from a lot of hands-on experience, it was maddeningly tedious to calibrate and the linear tracking mechanism fell disastrously out of alignment at the most Infinitesimal disturbance. This was especially problematic since simply playing a record was one of the Infinitesimal disturbances that threw it out of whack.