Smooch.io for Facebook Messenger - Message your customers from Slack, Front, a bot or anywhere!
SendX.io - SendX (https://sendx.io) provides remarketing and retargeting tools for web businesses. You can use popups, landing pages, email, web push notification, automation workflows and FB / Google retargeting to drive more revenue.
GetChat.App - Add WhatsApp chat to your website for free
Nova Inbox - Personalize emails in seconds, right from your inbox
Avochato - Text messaging for your business.
Brevo - Innovative online Email Marketing solution to manage your contacts, create & send your newsletters and track your results. More than 80 000 clients. Best prices and attractive features.