Doodle - Make meetings happen. With Doodle, scheduling becomes quick and easy.
Dialog Messenger - handy and feature-rich enterprise multi-device messenger available for server or cloud – Slack-like, but not Slack-limited
NeedToMeet - Schedule a meeting in a few clicks to find a time that works for everyone.
Ripcord - A desktop chat client for Discord and Slack
YouCanBook.me - YouCanBook.me is a cloud-based service which allows your customers to schedule appointments and make bookings.
Ziggs - Smoothly Share Content Between Devices!