Planmesh - The easiest way to plan with friends
Teamup Calendar - Cloud-based calendaring using capability URL, application developed in Zurich, Switzerland.
tripcake - Doodle for travel plans with friends
Campaign Calendar - Campaign Calendar by Bracket Labs builds a marketing calendar from your Salesforce Campaigns.
eezy - Daily adventures for ambitious people
ApPHP Calendar - ApPHP Calendar is a PHP calendar script that may be easily integrated and used with various PHP projects, such as schedulers, event, etc.