Fidget Spinner is web service that akin to a real fidget spinners doesn't do any useful work.
It has a single endpoint GET /spin which "spins" CPU for a bit faking useful
work. See it's OpenAPI doc.
As surprising as this might be this service has it's uses. It's raison d'être is testing of both Kubernetes horizontal pod autoscaling and cluster capacity autoscaling and their behavior under various conditions. More specifically CPU utilization or RPS based autoscaling.