Pulse SMS - Pulse SMS is a next-generation SMS and MMS application that is fast, secure and packed with lots of modern features as well as customization feature you cloud want.
Jasmin SMS Gateway - Jasmin is a very complete open source SMS Gateway with many enterprise-class features such as:
QKSMS - QKSMS is a beautiful communication app that offers magical texting experience.
Kannel - Open Source WAP and SMS Gateway
Textra - Textra is a seriously beautiful, feature rich SMS and MMS app.
Ozeki NG SMS Gateway - Ozeki NG SMS Gateway is a powerful, reliable and flexible SMS Gateway application.