Rotation of points is a very important aspect of patternmaking.
It's used in making darts and many other patternmaking methods.
The tool would prompt for a center point (rotation point), the point to be rotated, an angle, and direction (clockwise, counterclockwise).
It would be best if the angle could be specified as either an angle in degrees, or a function which returns the angle of a vector given by three points. e.g. -
angle(A1, A, A2) where A is the center point of the vector, and A1 & A2 are on 'rays' of the vector, the angle is < 180