Dialog Messenger - handy and feature-rich enterprise multi-device messenger available for server or cloud – Slack-like, but not Slack-limited
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.
Ripcord - A desktop chat client for Discord and Slack
Sendblue - Programmatically send iMessage and SMS
Ziggs - Smoothly Share Content Between Devices!
Hitch.ly - Turn any URL into a phone number you can call or text