Create two objects that rotate together when locked

I've been looking and looking trying to find this. What I want is to have two rigidbody objects so that when one is rotated, the other rotates in all 3 dimensions in the same direction - when they are locked together. When they are not locked, they don't rotate together, and when they become locked together again the following object doesn't "SNAP" to the x, y and z axis of the leader object, but continues to rotate with it from its current angle. So you could for example grab the following object, turn it, then let go and grab it again and turn it farther, etc.