Are you looking to give the workshop or attend it?
Free and Open Source Software
If it's free and open source and it's also software, it can be discussed here. Subcommunity of Technology.
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I'm thinking about offering some workshops. My local authority has funds available for courses and workshops which benefit the community, aimed particularly at people on low incomes. It would be fairly basic stuff, like where to access free software, the advantages of it, some recommendations and perhaps even some introductory lessons on using software like Libreoffice, Thunderbird, KeepassXC, GIMP, F-droid, the Fossify suite etc.
Depends on contents. Open source books exist. "The Carpentries" come to mind. Freecodecamp, Zines, etc too.
I can't imagine what that would be since FOSS itself is already so niche. Do you want to start such a program at your local library? That would be awesome!