More fragmentation isn't really a selling point of alternatives to a market player with a big critical mass and network effects.

Fluxer is still behind on Matrix with clients like Sable.

Sable used to be behind on Fluxer, but Sable made a lot of updates over the months, and Fluxer is more or less currently focusing entirely on the mobile app, while missing some rather important key features, like Federation and E2EE for private chats.

Fluxer is, however, far more easy to set up a self hosted server with. You cna get it done within an hour.

Good list, didn't know about armada yet. Will add one more: https://www.gamevox.com/