I am the developer of the Databag project [https://github.com/balzack], a federated + decentralized messenger. It currently has a smaller feature set than projects like matrix or mattermost, but does support the core features of sending text, image, audio, and video messages. Beyond privacy, the primary motivation for the project is to support low power hardware in the hopes of being embedded into consumer electronics, and therefore reach a much larger audience. Currently, the project has working instances of the backend node running on an intel nuc all the way down to a raspberry pi zero.
The messaging service has a browser app and a mobile app for both android and ios. I use this as the primary tool for communicating with my family but am hoping for more feedback from a larger user-base with diverse use cases. I believe listing the project in privacytools would increase its visibility and perhaps lead to some people interested in self-hosting giving it a try.
Let me know if listing the project is a possibility, or if anyone is interested in selfhosting the project themselves, and I will support any way I can. Thanks!