Smooch.io for Facebook Messenger - Message your customers from Slack, Front, a bot or anywhere!
WikiPro - All-in-one Business to Customer Communication
GetChat.App - Add WhatsApp chat to your website for free
Text Groove - Text enable your existing business landline, VoIP, or toll free phone number and connect with your customers in a whole new way. Try Text Groove for free.
Avochato - Text messaging for your business.
Heymarket - The professional way to text message. Your customers are mobile. Heymarket helps you manage those relationships from your smartphone.