Meet the Vortex Dome: a Rheoscopic fluid desk toy with magnetic needles that creates trippy patterns as you give it a spin. It ships with a tiny magnet to manipulate the needles. This was made by David Fowler. It measures 200mm in diameter. The below video shows how it works:
If you are up for DIY projects, you can always build one of your own. The Vortex Dome has a pretty clean design and doesn’t cause any mess as you play with it.