For practice typing code, choosing "quotes" mode and then using the advanced options to set a "language" to a computer language is a semi hidden feature.

The memory option under behavior -> funbox looks like an interesting challenge.

I really wish there was something like this that also drilled you on common keyboard shortcuts for your OS / desktop environment / commonly used programs. Like Vim Golf / Vim Racer, but for mainstream systems and applications.

I was introduced to MonkeyType a few weeks back and I think it's the best typinig site I've used so far. And it's open source!

https://github.com/monkeytypegame/monkeytype

I also like https://www.typelit.io/

Makes me feel like I'm writing a book.

http://typeracer.com is another fun one