The siltstone Sabu disk was discovered by Walter Emery in 1938 at the Saqqara Necropolis south of Giza. It is named after an official in whose mastaba tomb it was found. Dating from the First Dynasty around the 30th century BCE, few such objects have ever been found with a bizarrely modern, steering wheel-like design.
Because of its three unique lobes and arches with a hole and socket in the middle, archaeologists have provided competing theories as to its original purpose. These range from offering a tray (the most mainstream theory) to an oil lamp to even a spinning wheel. It was certainly too brittle to be used as a cartwheel. Some speculate that the design may be an imitation of a lost metal one.
Other even less plausible theories that are favorites outside of archaeology include that it was part of a lost ancient technology or even an alien artifact. Such proposals are often backed by claims that it could only be made with modern machinery. Not only is this not quite true, but the ancient Egyptians actually left behind depictions of how they made circular stone vessels. The real question is why they would specifically make a single object of such a shape.