Libre Lounge @librelounge has nice #podcasts on Libre matters, in particular a series on #ActivityPub, starting with "What is Federation" and then digging into it with a "Part 1 / 2 / 3" set: https://librelounge.org/archive/. #fediverse
A Mapstodon instance for the OpenStreetMap Community (English language)!
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Our francophone friends have a Mastodon instance: fr.osm.social