[est31]

I think this refers to server instances instead of server implementations.

[Arathorn]

It does - the point is that anyone can spin up their own Matrix server (or pick an existing one) and get involved; they don't have to use the fosdem.org one.

Separately, in terms of implementations: Dendrite is usable these days, albeit beta: https://matrix.org/blog/2020/10/08/dendrite-is-entering-beta, and meanwhile Synapse is stable. Conduit (https://conduit.rs) is making progress on federation (and works for simple use cases), and Construct (https://github.com/matrix-construct/construct) exists too.