First but not least there is the clasic grabber arm.

Whether used on its own or as part of a larger invention, the Grabber Arm provides practical functionality with an organic look. This is no accident: the design of the Arm is based loosely on that of a human limb. Angular beams attached to steering wheels open and shut much like an opposable thumb against fingers. Within its skeleton-like chassis, worm gears and axles flex frame segments just as tendons and ligaments bend a wrist. The motion is controlled by muscle (the motors), and the muscle is controlled by the brain -- in this case, the RCX.