When2Meet - When2meet helps you find the best time for a group to get together. It is a free survey tool that is quick and easy to use.
Cronofy - Unified Calendar API for developers
x.ai - x.ai is a tool to schedule meetings for you and your team.
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.
WhenAvailable - WhenAvailable is an excellent event management tool that allows scheduling the dinner party, book club meeting, and guys’ night out with simple and best ideas.
Calendarix - Calendarix is a powerful and easy to use web-based calendar that runs on PHP and MySQL.