Cron - Cron Calendar.
MIT License - A license from the Massachusetts Institute of Technology.
zcal - zcal is the fastest way to schedule every meeting for Free and make it personal.
Simplified BSD License - Also known as the "2-clause" BSD license, this is a simplified version of an open source license created at the University of California Berkley.
Cal.com - Cal.com (formerly Calendso) is the open source Calendly alternative.
AGPL - GNU Affero General Public License. Strong license for applications designed to guarentee user freedoms to access, modify, and redistribute server-side code.