For example WeChat, similar to WhatsApp which doesn't work in China, is a hugely popular app that is used virtually universally in China. Sure, there are other sites and apps that you can access to achieve many of the same objectives. This of course is a huge inconvenience for many US/Canadian travelers to China as we have become accustomed to relying so many apps and sites and in particular Facebook, Instagram, Gmail, Google Maps and WhatsApp and Skype. In addition, the vast majority of all non-Chinese websites are purposefully slowed down.
Apps such as Google Maps, Gmail, You tube, WhatsApp, Twitter, Facebook and many news websites including CNN, the WSJ, New York Times and many more are blocked due to this Firewall. The term that has been coined for this is the "Great Firewall of China." Many of the apps and websites that we use on an everyday basis are useless in China. Many sites simply are inaccessible in China due to a firewall. China has some of the world's most rigid restrictions concerning what websites you can and cannot access.