Avochato - Text messaging for your business.
indemandly - Live chat 2.0: Customer messaging that converts
Message Me - Website to create your contact business card
Slack with your Users - Speak to your app's users entirely within Slack
Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
StackWhats - Add the WhatsApp Live Chat to your website