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Tablet Android pen-drawing app
(beehaw.org)
If it's free and open source and it's also software, it can be discussed here. Subcommunity of Technology.
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It's currently in early development and I don't know how well it works, but Xournal++ mobile is a thing. Its desktop app is really good, so I'd expect the mobile app to eventually get there aswell.
Edit: Whoops skipped the drawing part, Xournal++ is more for note-taking. Krita is a good choice for drawing.