Spike.sh - Spike is an incident management platform that alerts via slack, phone and email and automatic escalations to help teams fix infrastructure problems.

Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.

Clerk - Clerk.io, the artificial intelligence for e-commerce that knows your customers interests.

Tidio - Tidio or Tidio Chat is an online chat software that combines messages from emails, website chat, and Facebook Messenger widget into a unified agent interface that allows agents to deal with all customer messages at the same time with the same tools……

Sendblue - Programmatically send iMessage and SMS

Free HelpCrunch Live Chat - Free live chat & in-app messenger for startups