Jasmin SMS Gateway - Jasmin is a very complete open source SMS Gateway with many enterprise-class features such as:
BlockSurvey - Privacy-focused surveys, polls & forms
Ozeki NG SMS Gateway - Ozeki NG SMS Gateway is a powerful, reliable and flexible SMS Gateway application.
Slack Surveys by Standuply - A simple, powerful bot for recurring surveys on Slack 📝
Kannel - Open Source WAP and SMS Gateway
Simple Poll - The easiest way to create polls in Slack