Vocabulary lists for most major textbooks. Downloading the lists requires free signup to Skritter. Read more.

skritter.com

This site contains a huge number of lessons, complete with texts, vocabulary, audio, exercises and much more. And it's all free. Note that if you want to get the intermediate and advanced material,... Read more.

collections.uiowa.edu

A website on the etymology of Chinese characters, with a lot of images of their past forms from different periods. Read more.

chineseetymology.org

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

You can input Charakters and this tool will output statistics about the words and characters, and can suggest high frequency words and characters that should be learned. It also analyses the HSK le... Read more.

hskhsk.pythonanywhere.com

The stories behind the names of all of China's provinces and autonomous regions. Read more.

online.thatsmags.com

A program to split any Chinese text into individual words, summarizing information about each unique word. The information is presented in the form of a tab-delimited matrix, so that the results ca... Read more.

zhtoolkit.com

This course is designed to give a practical command of spoken Standard Chinese. Nine situational modules form the core of the course. Each core module consists of tapes, a student textbook, and a w... Read more.

fsi-language-courses.org