Octane AI - Octane AI offers tools to create a bot and engage customers and audience via messaging.
GetChat.App - Add WhatsApp chat to your website for free
Dialogflow - Conversational UX Platform. (ex API.ai)
Smooch.io for Facebook Messenger - Message your customers from Slack, Front, a bot or anywhere!
Botkit - Botkit is an open source developer tool for building chat bots, apps and custom integrations for major messaging platforms.
Avochato - Text messaging for your business.