Movie Masher
Browser-based online video editor and encoding API
... decision lists, handling uploads and asset searching.
XML is also used to describe the GUI itself as well as its underlying functionality - there is no need to recompile the Flash applets! But if you so desire then custom fonts, effects and widget classes can be written in AS3 - PixelBender support too, for effects and transitions.
http://www.moviemasher.com