There have been a lot of Ajax calendar applications (see the events and calendar category in eHub). Spongecell differentiates itself with the Spongebar, a natural language processor embedded in the web UI that allows typed phrases such as “lunch with joe feb 3 at 1” to create a subsequent entry in the calendar. Of course, there’s also a mobile interface to send short queries and appointments.
I found the calendar fast and simple to use with a smooth feature to drag over several blank cells if an event spans multiple days. Events are edited by inline popup screens that cover the interface (a technique I first saw with Jalenack’s Ajax Periodic Table and which Max and I adapted for the Ajax gallery demos).
Other features include importing events and publishing an RSS feed, privacy and sharing with friends or the public. I wish the web interface had better screen resizing for the side panels. It’ll be interesting to see what’s unveiled at the launch party.