Ruby

These three Ruby tutorials rebuild well-known infrastructure, which makes them a good fit once you know the language and want to understand how the tools you use work. Build your own Redis by Rohit Paul Kuruvilla, a co-founder of CodeCrafters, is a 5-part series that builds a Redis server handling concurrent clients and the Redis protocol.

Rebuilding Git in Ruby, from thoughtbot, recreates Git's object storage and basic commands so you can see how blobs, trees and commits fit together. Build a Network Stack with Ruby works through the layers of networking by building them yourself in Ruby. Start with Redis, which has the clearest structure, then Git, then the network stack. Rails tutorials have their own section.