From what I've read, it looks like Kiko is different because it offers some fancy Ajax drag and drop features. Ajaxian has a good review of the features:

* Appointment reminders via email, text messages, and AIM * RSS feed for upcoming events * Natural Language Quick Create (ex: "3/26 2am Raid on Ironforge [WoW] +thrall +gromhellscream") * import appointments and contacts via iCal and vCard * and personal public URLs for your calendar.

Here's some screen captures taken from Kiko...