One thing I've enjoyed doing is taking projects with a permissive license, e.g. MIT or Apache and rewriting them in my language of choice. To start with it's a

One thing I've enjoyed doing is taking projects with a permissive license, e.g. MIT or Apache and rewriting them in my language of choice. To start with it's a mechanical exercise in transcription but you begin to learn more about the problem domain and get ideas for side avenues and questions to explore. And at the end of it all you've enriched an ecosystem and can give any improvements back to the original project.