Time.ly - Time.ly is a collaborative calendar solution for websites.
Teamup Calendar - Cloud-based calendaring using capability URL, application developed in Zurich, Switzerland.
CalendarX - Get a calendar your audience can follow
Google Calendar - Spend less time managing your day & more time enjoying it
Campaign Calendar - Campaign Calendar by Bracket Labs builds a marketing calendar from your Salesforce Campaigns.
Kin Calendar - The simple and connected calendar