Bocker
Docker implemented in around 100 lines of bash
...With bocker you can perform basic operations such as pulling an image, running a container, exec into a container, listing containers, and removing them. Because it's written in shell, it is easy to read, reason about, and adapt for experiments or instructional use. It is not intended for production use due to performance, security, and missing features, but it is a useful tool for learning how containers work under the hood. Many learners and educators reference it when teaching container internals or when debugging container behavior in a minimal environment.