I checked out SpongeCell, which is yet another online calendar application, and I found it to be a really beautiful example of what can be done with AJAX. The HTML effects being used and the workflow of the application are very well done. Not only that but I've read on TechCrunch that this site is based on Ruby On Rails.

There are a couple of things I wonder about from a technical prospective with SpongeCell. I wonder how they are dealing with accessibility issues with an application using AJAX as extensively as they are here. I just can't see things working anywhere near as well without it. How the technical team would compensate for the lack of it would be no small feat. Also, they have a feature to setup email alerts based on scheduled events in your calendar. As I have mentioned previously with a Rails application it is not possible to do such things without the help of some sort of external scheduler.