Ask HN: Side projects to better understand distributed computing

I'm looking for ideas for a side project which will allow me to build skills and familiarise myself with distributed computing concepts. More specifically, I want to develop software which allows me to flex my abilities in distributed concurrent systems. However, I can't think of a solid use case in a side project at home, does anyone have any ideas?

I'd love to be able to deal with scaling my service on aws, be concerned with concurrency in a system, and delve into improving system performance... But I've never worked on a system that allows me to learn these skills therefore I'm looking for a side project which will allow me to develop such a skillset.