Rotator

This block could attach to blocks like sticky pistons do (treating them as one big block when connected by slime/honey). When powered by redstone on one side, it could turn clockwise by a small amount, and when powered on the other side, it could turn counter-clockwise by a small amount. When broken, it could reset the structure to its original orientation. This would be useful for builds like windmills, ceiling fans and vault doors.