It is a Java servlet that implements calendar. You can use it as a standard calendar system, for booking some resources etc. Calendar supports WAP/WML so you can use it even from your mobile phone.

Calendar's users may by notified by e-mail about schedule changes.

Calendar supports file based persistence - your data will be saved in the flat file (files) or database based persistence.  

Try it Out: http://www.servletsuite.com/servlets/calendar.htm