Originally designed as a stress-relieving tool, they have even been used to help children with additional needs such as ADHD.
They're like little propeller-shaped gadgets with ball bearings that allow them to spin.
Kids enjoy competing to see who can come up with the best tricks or keep their gadget spinning the longest.
They can also help kids focus on daily tasks, and relieve anxiety levels.
This multi-mechanism is billed as 'great for those that can't quite keep still and need a fidget phenomenon to stop the strains and stresses whilst working'.
There's also a bit of science to it and some tricks you can perform using stuff like hair dryers.