25DaysOf - A customizable advent calendar, for everyone
Google Calendar - Spend less time managing your day & more time enjoying it
Frozen Goodies - An advent calendar to get the chance to win daily prizes
Simple Calendar - A simple calendar with events (optional recurring and reminders), week numbers and a customizable...
Syndical - Automatically publish events across a range of platforms
Calendar Lock PEA - Calendar Lock PEA is an encrypted desktop calendar with a day, week and month view. The shown calendars are never stored unencrypted on your disk, but exist only in the RAM. Platform-independent, Open Source, no installation or registration required.