MOCpages user David Hyman created an ambitious Lego robotic hand controlled by a wrist-mounted exoskeleton packing 3 rotation sensors and 2 touch sensors.
I built it using 3 RCX bricks, one for each finger. The hand has two fingers and an opposable thumb. Each finger/thumb uses a rack & pinion mechanism which moves flexible tubes attached to the fingertips. Feedback is given by light sensors and a gradient attached to the toothed rack. It is controlled by a skeletal hand that you wear, with rotation sensors for the fingers and touch sensors for the wrist.
It can pick up balls and other objects and manipulate them quite easily. Its quite funny to watch other people using it! The system requires you to hold your hand steady – the robot will copy you exactly – if you don’t, it can be hard to hold objects properly.