Quoting from the article:

The openEngiadina project is developing a platform for open local knowledge. With regard to technology, this has so far consisted of:

• Research into a suitable data model:
  • How to use RDF for various types of data (including ActivityStreams for social interactions)
  • How to make RDF content-addressable
  • A scheme for robust content-addressing
  • How to cryptographically sign content-addressed content
  • How to use CRDTs for mutability (this work has been continued as part of the DREAM project)
• Development of a client for creating and curating content: GeoPub
• Development of a server capable of handling of such diverse types of content: CPub

[…]

Over the last couple of months we have been exploring XMPP as an alternative to ActivityPub and are happy to announce an initial proof-of-concept version of GeoPub - the openEngiadina client - using XMPP. You can try it here (an XMPP account is required). The source code is available on Codeberg.