I run public servers for Glasgow for some of the decentralised projects I find interesting. Most of them use the ActivityPub protocol.
I've experimented with PixelFed and PeerTube, but decided not to devote the resources to running them publicaly.
I also run a Wiki for Glasgow. While it isn't decentralised, all the data is available as both a download and a Gemini site: gemini://wiki.glasgow.social
I'm collecting some links that sum it up better than I can: