Here's a neat GitHub feature that I haven't noticed before: if you hover over Contributors, it shows you profile pictures of major contributors!
This picture is from https://github.com/github/semantic.
Reminds me of JS projects that generate READMEs with this visualisation.
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It's weird that GitHub shows time since the last commit, but not time since the first commit. It's a nice way of seeing how mature a project is.
One cute feature of markdown I'd not noticed before: there's no syntax for images *without* a description (i.e. alt text).

https://spec.commonmark.org/0.31.2/#images
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?