Teamup Calendar - Cloud-based calendaring using capability URL, application developed in Zurich, Switzerland.
Houseparty - Brining empathy to online communication.
Campaign Calendar - Campaign Calendar by Bracket Labs builds a marketing calendar from your Salesforce Campaigns.
Booyah - Video chat with up to 12 friends at the same time.
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.
Slack - A messaging app for teams who see through the Earth!