$$\begin{array}{ll} \mathbf{\text{Left Button}} & \text{add point} \\ \mathbf{\text{Right Button}} & \text{move the closest point}\\ \mathbf{\text{Del}} & \text{remove last point}\\ \mathbf{\text{Ctrl-S}} & \text{print list of points to console} \end{array} $$
An initial list of points can be loaded from a file indicated as a command line option.