Cronofy - Unified Calendar API for developers
Planmesh - The easiest way to plan with friends
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.
tripcake - Doodle for travel plans with friends
Calendarix - Calendarix is a powerful and easy to use web-based calendar that runs on PHP and MySQL.
eezy - Daily adventures for ambitious people