Cronofy - Unified Calendar API for developers
Raft Calendar - A fun and beautiful calendar for couples and close friends
Calendarix - Calendarix is a powerful and easy to use web-based calendar that runs on PHP and MySQL.
Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Campaign Calendar - Campaign Calendar by Bracket Labs builds a marketing calendar from your Salesforce Campaigns.
emble - Plan better events with your friends