Another Microsoft creation—this time from the mad geniuses at Microsoft Research— Blink Cliplets "lets you exercise your creative talents by layering static and dynamic visual elements," as its description puts it.
What does that mean? Basically, the app lets you upload a video clip, choose a frame from it to set as a static image, and select elements of the video to leave in motion over said static image. For example, you could have a (mostly) still picture of an Italian fountain in which the water actually flows.
Yeah, it sounds weird, but Blink Cliplets is an absolute joy to play around with, easier to use than you'd think, and best of all, totally free. Check it out.