Most Advanced Calendar Application
Smart PHP Calendar is a user friendly, ajax based and multi-user calendar/scheduling application. It has so many great features like timeline, multiple calendars, shared calendars, event drag & drop, iCal import/export, overlap/double booking prevention and so on. You can customize it easily and use as a standalone scheduling application or integrate into your own application. You just need a web browser or HTML5 supported mobile device to use it. You can sign up or install to your own server.