eezy - Daily adventures for ambitious people
Cronofy - Unified Calendar API for developers
tripcake - Doodle for travel plans with friends
Campaign Calendar - Campaign Calendar by Bracket Labs builds a marketing calendar from your Salesforce Campaigns.
DUNK - Surprise your friends with secret group plans
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.