Google Contacts - Google Contacts is Google's contact management tool that is available in its free email service Gmail, as a standalone service, and as a part of Google's business-oriented suite of web apps Google Apps.
Cronofy - Unified Calendar API for developers
Free Address Book - In our contact management software you can store fast and easily name, phone numbers, birthdays, address, company name, city, mobile numbers, insurance and loan info, e-mail addresses.
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.
Clearbit - Clearbit provides Business Intelligence APIs
Calendarix - Calendarix is a powerful and easy to use web-based calendar that runs on PHP and MySQL.