It's really fun to look up super obscure open source projects. I look on the AUR, Github, Gitlab, and sometimes just a simple search. Here is one I found that I thought is kinda interesting:

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Makerdon is a Mastodon instance focused on Makers, Open Source Hardware (OSHW) and STEM/STEAM. Free and Open Source Software (FOSS) is a likely topic as well. If you're interested in making things, allowing others to build on your work, and/or teaching others about making things, you might like this instance.