Timekit - The developer-friendly scheduling & booking solution

Cron - Cron Calendar.

Roombelt - Roombelt displays details about the current and upcoming meetings right at the confluence room door. Say goodbye to meeting interruptions and double reservations in your office.

zcal - zcal is the fastest way to schedule every meeting for Free and make it personal.

RobinPowered - Robin coordinates meeting spaces, people, and things in your office. Complete with analytics and insights that uncover usage and help optimize space.

Cal.com - Cal.com (formerly Calendso) is the open source Calendly alternative.