I use the QQ messenger program from Tencent in China. While its big brother WeChat has a very broad ecosystem, QQ is much smaller and has limited function. As I wish to limit such a program to only messaging people in China, QQ fits the bill for me. Both QQ and Wechat are standalone programs that can run on Windows, Mac or Android. There is no version for Linux.
Both QQ and WeChat have a huge following in China. QQ has 805.5 million users, while WeChat has 1,040 million monthly active users (MAU). As of the second quarter of 2018, Facebook had 2.23 billion monthly active users [worldwide].