Not really a new idea, but I really like those print-in-place herringbone planetary gears, the most famous probably by Emmett. They are really nice fidget toys and a great demonstration of what 3D-printing can do.

For this version however I used a completely different method to achieve these more rectangular teeth and well working planet gears with only 3 teeth (actually also 2 teeth are possible, but they don't run that smoothly).

Included are 3 versions with different tolerance settings; tol20 should be ok, if you find it too loose, try tol17.

The gears might need to be broken free individually with a bit of force; if that doesn't work, try a bigger tolerance.

The center hole fits a standard tool bit, you can use a power screw driver to break the gear in for smoother operation.

If you like interesting uncommon gear fidget things, try the "binary sun gear".