WeChat is a dominant chat app in China especially for 20ish ~40ish. And these years even my gradma and gradma are using it. And it is not only a chat app but also tied to many other lifestyle apps/services, like paying the utilities, buying movie tickets, ordering food and so on.
I'm fascinated by what publishers are doing on big messaging platforms to reach new audiences. WeChat, which is enormous in China, has seen some very cool experimentation from BuzzFeed, the Wall Street Journal, and others.