Mixmax Calendar - The fastest way to schedule meetings with anyone, anywhere
Cronofy - Unified Calendar API for developers
Meetingbird for Gmail - View your calendar and schedule meetings right from Gmail
Campaign Calendar - Campaign Calendar by Bracket Labs builds a marketing calendar from your Salesforce Campaigns.
Calendly - Say goodbye to phone and email tag for finding the perfect meeting time with Calendly. It's 100% free, super easy to use and you'll love our customer service.
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.