RawShorts helps people create beautiful explainer, demo and
marketing videos for web with an easy to use drag and drop video builder
in the cloud. The free account allows you to distribute the link to your video, but you can't download it to your computer (screen casting it, though, is an easy work around). With the free account you get 25MB of space and a maximum video length of 3 minutes. This would be an ideal tool for classroom "commercial" type assignments.