Oh so cool and nifty! The idea is real simple, just a (or many) flat disk(s) with a gas or a liquid shooting across at a tangent.
A Tesla turbine is a quite unique technology. It was invented and patented by Nikola Tesla on the 21st October 1909 at the Untied States Patent Office from experiments done in England. The patent 1061206 was granted on the 6th May 1913. Although, it is thought that a Tesla first showed a 200 hp 16,000 RPM version on the 10th of July 1906 (on Tesla’s 50th birthday).
Tesla Turbine