A number of years ago for one of my design courses at Otago University, we were instructed to design and build a toy for visually impaired children. We had a speaker come in and tell us all about the different aspects of assisted learning for kids with visual impairments. One thing that is very important in their development are toys that stimulate wrist rotation. This assists with motor development and strengthens muscles that would normally be exercised through hand-eye coordinated movements. What I came up with was an encased gyroscope. It allows the holder to turn their wrist only on a single axis, and also makes a neat whirring noise and slight vibration that might intrigue someone who couldn't see it. The gyro is easiest to describe as a yo-yo encased in a pair of clamshell-like covers.
The prototype I turned on a metal lathe, using brass for the flywheels, and aluminium for the clamshells. The clamshells are attached by a single shaft through the middle, and can't rotate independently of one another. The two flywheels are attached by a tube, and the clamshell shaft passes through this tube. The inside and outside are only connected by a pair of bearings which allows the internal flywheels to spin while the outer shell remains stationary.
In order to use the gyro, you wind a cord around the middle like a yo-yo and pull it out like a ripcord to start the wheels spinning.
Since completing the project I learned of a product called the NSD Powerball
which operates on basically the same principal, but has a dynamic gyroscope axis, rather than a fixed one like in my design.