I wonder what other "computing"-type side project ideas are out there in which one would refine their programming skills (as opposed to interest-based projects like an app to do X or projects with monetization potential).
Examples off the top of my head:
- Make a programming language
- Build a database or query language
- Build a kernel module
- Implement a protocol (TCP, HTTP, UDP)
- Write code in a functional language
- Implement Git
What other ideas fall into this category?
- Build a package manager
- Create a linter
- Build a static code analyzer / function call graph generation tool
Actually, I think it's more interesting to focus on one and dig deeper.