Windows Contacts - Windows has many extraordinary organizers, and in the event that you include distributed storage, then you presumably have more.
Cron - Cron Calendar.
Flexibits - Makers of Cardhop, Chatology, and Fantastical.
zcal - zcal is the fastest way to schedule every meeting for Free and make it personal.
Apple Contacts App - Access and edit your contacts from personal, business, and other accounts with the Contacts app.
Cal.com - Cal.com (formerly Calendso) is the open source Calendly alternative.