Dialog Messenger - handy and feature-rich enterprise multi-device messenger available for server or cloud – Slack-like, but not Slack-limited
Doodle - Make meetings happen. With Doodle, scheduling becomes quick and easy.
Ripcord - A desktop chat client for Discord and Slack
NeedToMeet - Schedule a meeting in a few clicks to find a time that works for everyone.
Done Hui - No need to switch between multiple pieces of software to get through the workday. CHATS: Communicate freely. CALENDAR: Know your team's availability, plan meetings. No more conflicts. TO-DOs: Stay on top of all projects. FILES: All files, one spot.
YouCanBook.me - YouCanBook.me is a cloud-based service which allows your customers to schedule appointments and make bookings.