Openfire - Openfire (formerly Wildfire) is a cross-platform instant messaging (IM) and groupchat server.
ShoutOUT - All in one business texting tool to send personalized alerts, promotions, reminders, short links and marketing campaigns, for any SMEs (hotels, restaurants, education, non profits, Woocommerce, banks, healthcare, agencies, supermarkets, weddings)
Prosody - Prosody is a modern flexible communications server for Jabber/XMPP written in Lua.
Trumpia - SMS Marketing and Marketing Automation software for Mass SMS, internal communications & emergency alerts. #1 Text Messaging Service used by Fortune 500s.
Matrix.org - Matrix is an open standard for decentralized persistent communication over IP.
Clickatell - Simple, reliable mobile messaging cloud.