Lightning Calendar - Organize your life — it’s about time!
Kin Calendar - The simple and connected calendar
Simple Calendar - A simple calendar with events (optional recurring and reminders), week numbers and a customizable...
Google Calendar - Spend less time managing your day & more time enjoying it
GMinder - GMinder is an open source Windows System Tray app that pops up to remind you about Google Calendar events.
Teamup Calendar - Cloud-based calendaring using capability URL, application developed in Zurich, Switzerland.