Time.ly - Time.ly is a collaborative calendar solution for websites.
Google Calendar - Spend less time managing your day & more time enjoying it
CalendarX - Get a calendar your audience can follow
Teamup Calendar - Cloud-based calendaring using capability URL, application developed in Zurich, Switzerland.
Campaign Calendar - Campaign Calendar by Bracket Labs builds a marketing calendar from your Salesforce Campaigns.
Microsoft Outlook - Organize your world. Outlook’s email and calendar tools help you communicate, stay on top of what matters, and get things done.