BlueIgnis hosts an invite-only Matrix instance. Matrix is a decentralized & federated communication protocol created to provide open and secure text, voice and video chat for everyone.
The reference implementation Synapse can be selfhosted (and custom implementation can be written by everyone) which makes it an incredible interesting and valuable project.
Even through our server is private, it’s still federated, which means that users from other instances can chat with users on our instance and viceversa. You can learn more about over at Wikipedia.