VMMap saves each snapshot and allows you to view the differences by selecting the Show Changes entry in the Options menu. When you toggle to that mode, the status bar shows the times of the refreshes being compared and the summary and details lists shows the differences between them. VMMap shows address ranges that are in the most recent snaphot but not the previous one with a green highlight color and those that were deleted in red. You can toggle back to viewing the statistics of the most recent snapshot by deselecting the option.
You can view differences between any two snapshots by opening the Timeline dialog, clicking the mouse and dragging the selection region between the two points of interest.