Talkus - Chat with your website users from Slack
GetChat.App - Add WhatsApp chat to your website for free
Slacking Pigeons - Chat in real time with your users directly from Slack
Smooch.io for Facebook Messenger - Message your customers from Slack, Front, a bot or anywhere!
Avochato - Text messaging for your business.
Slaask for Social Networks - Chat with your customers on Facebook and Twitter via Slack!