I haven't gone this far, but I get the same joy out of little side project CLIs and libraries. In particular I've written a CLI framework and a few apps with i

I haven't gone this far, but I get the same joy out of little side project CLIs and libraries. In particular I've written a CLI framework and a few apps with it. The apps' requirements stretched the framework's capabilities, so I've rewritten large parts of it over the years. It's incredibly satisfying to feel myself get better as a developer as I write and consume and improve my libraries.