GoAnimate is a browser-based animation studio. It lets you build multi-scene animated creations, complete with support for music, transitions, and user-uploaded page elements. I spent most of this morning playing around with it and the results are about on par with what you'd find on one of those animated greeting cards.
Like most video editing applications GoAnimate centers around a time line. Everything is drag and drop, so you can pick out characters, props, backgrounds and special effects and simple put them on the canvas where you see fit. Each "scene" can be edited to last as long as you want, and you can drag finished scenes around the time line to re-order them. Basically everything is set up to let you quickly clone and continue your work with minimal effort.
The short I made consisted of nine scenes and took about a half hour to make, however most of that was me learning how to use the tool. Part of the process is picking out ready made characters and customizing them which is fairly intuitive and similar to working on a Microsoft PowerPoint presentation. As the author you can move objects up and down, and program in things like automated object movement and transitions.
One cool feature is that you can upload pictures from your hard drive, Facebook, or Flickr and turn them into props, backgrounds, or human heads. These heads can be stuck onto the bodies of pre-made characters, so with just a few head shots you can make your very own animated faces by splicing scenes together.
While simple to use, the tool is not without its shortcomings. For instance, you can't set up several character movements or actions within one scene. This means attaching a speech bubble to a character requires its own scene instead of being able to time out multiple speech bubbles in one scene using delay. I know this seems like a small quibble, but it means adding in more scenes when you could simply mark out the action on a separate time line.
The tool also feels a little cramped on larger screens as it doesn't scale to match the extra width. This, too, is a small quibble, but after having played with Flash game creator PlayCrafter yesterday (story), tools that account for this extra space make it far easier for people who are serious about using them as an alternative to desktop applications.
GoAnimate is completely free to use. You can see an example of the test one I made here.