Teamup Calendar - Cloud-based calendaring using capability URL, application developed in Zurich, Switzerland.
Kin - Kin is money for the digital world. It is used to generate value through a shared, decentralized cryptocurrency in a digital ecosystem of apps and their users.
Campaign Calendar - Campaign Calendar by Bracket Labs builds a marketing calendar from your Salesforce Campaigns.
Plan - Plan is a better way to organize.
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.
Clean Google Calendar - Makes Google Calendar look nicer & launches as a desktop app