Greasemonkey - Customize the way a web page displays or behaves, by using small bits of JavaScript.
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.
Violentmonkey - Violentmonkey is a userscript manager to support running userscripts in web pages.
Doodle - Make meetings happen. With Doodle, scheduling becomes quick and easy.
GreaseKit - GreaseKit is a SIMBL plugin, that adds user scripting to Safari, Mailplane, Diet Pibb.
YouCanBook.me - YouCanBook.me is a cloud-based service which allows your customers to schedule appointments and make bookings.