Doodle - Make meetings happen. With Doodle, scheduling becomes quick and easy.
Cron - Cron Calendar.
Standuply - Run daily standup meetings and track your metrics in Slack
zcal - zcal is the fastest way to schedule every meeting for Free and make it personal.
MeetNotes - Increase Productivity with Meeting Notes Tool. More effective minutes, Prepare Agenda, Collaborative Notes & Action Items.
Cal.com - Cal.com (formerly Calendso) is the open source Calendly alternative.