Writing chinese characters
It would be nice to exercise writing charecters in duolingo as part of the lessons. The app "HelloChinese" offers this, but that app is not adaptive. Brain imaging research has shown that knowing how to write is an essential element of reading in Chinese: it helps recognizing the characters. I do write on paper with pen as well as brush, but integrated in duolingo it would help a lot.
Try using the Windows 10 app Lingvoji. You can use pen, touch, or mouse for handwriting exercises.