This site is best described as a Chinese version of Quora, so in other words a site where people ask and answer questions (and discuss other people's questions and answers). Read more.

zhihu.com

This is the best overview of spaced repetition research I have seen online or offline. It's thorough, well-argued and probably covers more than you were looking for. It's not specifically about Chi... Read more.

gwern.net

Douban is one of the most popular online Chinese communities and forums. You can read a wide variety of material - on almost any topic imaginable - from native speakers. It's a wonderful source... Read more.

douban.com

HSK Course is an online platform for HSK preparation. It aims to help you not only successfully pass the exam, but gain confidence in using Chinese language. It mainly has 3 parts: Grammar Les... Read more.

hskcourse.com

This is a Q&A page where teachers answer questions about Mandarin, mainly vocabulary use and grammar, but sometimes other questions as well. It's mostly useful because of the wealth of information ... Read more.

hwjyw.com

HiNative is a Q&A site where you can ask people all over the world about culture, language, anything. We support over 100 languages. Read more.

hinative.com

*The following introduction was written by John Renfroe and published here: [Learning Classical Chinese is for everyone (no, seriously!)](https://www.hackingchinese.com/learning-classical-chinese-... Read more.

amzn.to

This blog provides in-depth explanations of some grammar and vocabulary topics in Mandarin Chinese. While there aren't a huge number of articles so far, there are enough to issue a general recommen... Read more.

mandarinfriend.wordpress.com