Dialog Messenger - handy and feature-rich enterprise multi-device messenger available for server or cloud – Slack-like, but not Slack-limited
Adamant Messenger - The most secure and anonymous messenger, encrypted with Blockchain
Ripcord - A desktop chat client for Discord and Slack
Sonar - 2-way chat with your customers over SMS and FB Messenger
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.
ttirik - Unsure about giving out your phone number, but still need to make a call?ttirik is a free service that allows you to make calls with just a URL link.