from official docs:
https://github.com/ergochat/ergo/blob/stable/docs/USERGUIDE.md
Ergo integrates a "bouncer" into the server. In particular:
Ergo stores message history for later retrieval.
You can be "present" on the server (joined to channels, able to receive DMs) without having an active client connection to the server.
Conversely, you can use multiple clients to view / control the same presence (nickname) on the server, as long as you authenticate with SASL when connecting.