Nice start, but needs a lot of work. The file information it puts at the top is HUGE, there is no way to tell it basic things like "do 4 thumbnails across by 20 down, each 400px wide, and adjust capture timing to fit" or "do 10 thumbnails across, each 200px wide,, and make the image as long as necessary to catalog the entire video", or "do the same, but split into separate contact sheet files every 70 thumbnails", or whatever. It only provides a few pre-ordained options. Can't drag-drop into the application, only onto its icon. Can't save the contact sheet to the same directory as the video (should be the default behavior, but not even an option). Forget fancy features like being able to constrain the exact dimensions of the thumbnail images in the sheet, to fix incorrect aspect ratio. Developer: Please, just copy the standard features of typical Windows thumbnailers, and you'll make the app we actually want.
On the plus side, this is adequate for creating some basic thumbnail sheets just for cataloging your Movies folder or something, and it is very fast.