Coolendar is a slick natural language online calendar
When you think about it, a calendar is basically a to-do list with dates. Sure, we're used to looking at it in a certain format – all of those little squares, one per day. But coolendar takes the concept of a calendar and strips it from that familiar representation, leaving just a neat, carefully dated to-do list in its wake.
Visually, it's very cool. It's got that iPhone-app aesthetic that seems to be the new Web 2.0 look. All the buttons are rounded, the whole thing is colored in lovely pastels, and when you hover over a button, you get a funky "zoom in" effect.
A part of coolendar's claim to fame is its ability to parse natural language. So you can write "9PM Sunday, do something," and it correctly guesses that you mean next Sunday. However, this is something that Google Calendar already does, and I believe it does it a bit better than coolendar. For instance, coolendar had trouble with a perfectly clear request such as "Sunday in two weeks, do something." It's also lacking any sort of support for recurring events.
In short, the nicest thing about this app is the UI and the visual appeal. In terms of functionality, both Google Calendar and Remember The Milk have it squarely beat, at least for now.