Interesting project that got featured in HN today - https://codecrafters.io/ Basically they are saying that you can implement these kind of serious code with them (slightly guided I believe). There is a famous github repo

Build your own X

originally maintained by him - https://github.com/danistefanovic but now it seems that this company owns that repo https://github.com/codecrafters-io/build-your-own-x 😐