It's easy to observe software getting slower over time. It's nice to periodically reflect on software features that have become faster: sound codecs, JS execution, CSS engines.
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For hobby projects, I really like software where I can do small features or tweaks. Sometimes I don't have time for anything more substantial.
Website projects are great for this. Are there other areas?
Learning software development through playing and contributing to a MUD: https://tashian.com/articles/how-i-learned-to-program/
Do any tech streamers try new software live? It'd be a really fun way of doing UX testing.