Jasmin SMS Gateway - Jasmin is a very complete open source SMS Gateway with many enterprise-class features such as:
Estherbot - Transform your resume into a bot.
Ozeki NG SMS Gateway - Ozeki NG SMS Gateway is a powerful, reliable and flexible SMS Gateway application.
Scout - Scout ♥ monoliths.
Kannel - Open Source WAP and SMS Gateway
Gloat.com (prev. Workey) - Anonymously discover career opportunities with AI