HTML5 represents a significant move forward in Web development because it can provide those features by using the client system's browser, processor and memory to handle most of the heavy lifting. Previously, the limitations of older browsers and prior versions of HTML meant that either the server would have to do much of the processing, or the browser would need a plug-in or add-on to access the dynamic content.
The newest entry to this class of applications is Adobe's much-anticipated Edge. Well, new in the sense that it's not officially released yet. The first alpha (Preview 1) came out in August 2011; currently, users can download Preview 3.
Edge has an interesting provenance, given that it's made by the same company that has driven the very technology that HTML5 is trying to replace: Flash. Because of this heritage, you would expect Adobe to spend a lot of time making sure Edge is a top-of-the-line animation tool. And so far, it definitely seems to be on track. Even in this early iteration, Edge is an extremely powerful application.
Of the three standalone applications reviewed here, Sencha Animator has the distinction of being the oldest -- the first developer pre-release was announced in October 2010. It's a small distinction, given the rapid releases of many tools in early 2011, but it at least gives it the status of being first.
Another tool that gets high marks in the HTML5 animation world is Tumult Hype, a Mac OS X-only tool that makes good use of the OS X interface to build animations without the need to type in code.
If you are a Mac user, Hype is going to appeal to you immediately because of its interface. The use of the separate Inspector window is old ground to OS X users. While I can appreciate the flexibility to customize the interface by shifting its tools around (which you can't do in Animator), this is not a big selling point.