Smooch.io for Facebook Messenger - Message your customers from Slack, Front, a bot or anywhere!
Message.io - Make your chat bots cross-platform
GetChat.App - Add WhatsApp chat to your website for free
Chatfuel - Chatfuel is the best bot platform for creating an AI chatbot on Facebook.
Avochato - Text messaging for your business.
impossible.bot - Get a chatbot without writing code or any special content