Robosketch
From the site
Rotosketch is quite simply an intuitive tool for sketching, doodling and notating on top of video, such that the marks that are made are linked in time with the video. This allows the user to draw strokes along the the axis of time, as well as the normal x and y axes, and for those strokes to augment, analyze, interpret, or even obliterate a video sequence.[via]You can download it here