I actually build minimal Redis clones in every new language or runtime, or when I want to explore threading models.

It all started with https://github.com/rcarmo/miniredis (which I forked to add and experiment with pub/sub), and I just found myself doing it again and again because Redis is the quintessential network service:

By implementing it, you learn about socket handling, event loop for a specific runtime, threading models, data representation, concurrency (if you want to do a multi-threaded version), etc. None of my "ports" are fully functional, but they all helped me sort out some of the above plus build tools, packaging, dependencies, etc.

It's "hello world" for core cloud native microservices, if you will (and without having to do REST or JSON stuff).