Open Source Scheduling Software

Calendly

Python-based continuous integration testing framework; your pull requests are more than welcome!

Scheduling infrastructure for absolutely everyone.

Meeting poll tool

Rallly is an open-source scheduling and collaboration tool designed to make organizing events and meetings easier.

SOGo is a very fast and scalable modern collaboration suite (groupware). It offers calendaring, address book management, and a full-featured Webmail client along with resource sharing and permission handling. It also makes use of documented standards (IMAP, CalDAV, CardDAV, etc.) and thereby provides native connectivity (without plugins) to many clients such as Microsoft Outlook, Apple iCal, the iPhone, Mozilla Lightning, and a plethora of mobile devices.