There is no closed source Matrix server implementation that I'm aware of. Synapse is the server used in production for matrix.org, the French government deploym

There is no closed source Matrix server implementation that I'm aware of. Synapse is the server used in production for matrix.org, the French government deployments, and tons of other servers including my own. It is somewhat resource intensive but it can scale using workers. There is of course several other server implementations in progress but none are fully ready yet.