In this video, Ben Uyeda of HomeMade Modern demonstrates how to build a sleek, contemporary spiral staircase using just a standard schedule steel post, plywood and a CNC router (along with a healthy amount of wood and construction glue). To build the staircase, Uyeda uses the CNC to cut out 12 shapes of incremental size from a plywood sheet, which he then stacks and fits around the post to secure into place.
HomeMade Modern has also made the CAD files available for free, so handy woodworking types can attempt the construction themselves.