Cal.com | Open Scheduling Infrastructure
Calendly - Scheduling appointments and meetings is super easy with Calendly.
CoreUM - The Ultimate Meeting Application
Create your own polls - Terminplaner 4.1
Easy!Appointments – Open Source Appointment Scheduler
Meetin.gs - Free, Easy and Better Online Meeting Organizer
Meetsy
PeachPay - Monetize your Content
Polymail — Email Tracking, Templates, Send Later, and Calendar Integration
World Time Buddy - Ridiculously easy world time and meetings across time zones!