Two open source projects with great documentation
esbuild and Redis1 are two examples of codebases with exceptional documentation. Through their READMEs, changelogs, architecture documents, and code comments, both projects explain their design in such a way that someone new to the codebase can understand where things are, how things are done, and why they are done that way. If you’re a developer looking to get better at documenting your code and software architecture, these are great case studies.
https://johnjago.com/great-docs/