Appointment Booking Calendar - With the Appointment Booking Calendar you can accept online bookings from a set of available time-slots in the calendar.
Okta - Enterprise-grade identity management for all your apps, users & devices
MakePlans - Online appointment booking - MakePlans
Auth0 - Auth0 is a program for people to get authentication and authorization services for their own business use.
Dudle - Dudle is an online scheduling application, which is free and open source.
OneLogin - On-demand SSO, directory integration, user provisioning and more