I've never used iCal, but I've never met a Mac owner who doesn't. Since iCal is Mac-only, Borja Sanchez Zamorano decided to create a clone in .NET that runs on Windows or Linux using Mono called MonoCalendar (get it?). "Clone" might not be entirely fair, since Zamorano says "MonoCalendar does not try to be a iCal substitute," but rather a substitute for the Macless. MonoCalendar seems to be making rapid progress and sure looks like iCal, so if you've been looking for a calendar app that feels like iCal, it wouldn't hurt to check it out.