Raft Calendar - A fun and beautiful calendar for couples and close friends
Cronofy - Unified Calendar API for developers
Ddays - Plan events with friends without the back and forth messages
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.
Evedo - Events done better
Calendarix - Calendarix is a powerful and easy to use web-based calendar that runs on PHP and MySQL.