https://www.cnbc.com/2019/02/04/what-is-wechat-china-biggest-messaging-app.html

WeChat is China's most popular messaging app with a monthly user base of more than 1 billion people.

But it's unlikely that you would have used it if you live outside China. It is owned by Tencent, one of Asia's largest companies by market cap. While it started out as a messaging service, it has transformed into an app where you can do everything from payments to hailing a ride, or even booking flights.