It's "federation-as-a-service", basically. A common use case is federation between two Slack teams (share a channel). Another common use case is federation be

It's "federation-as-a-service", basically. A common use case is federation between two Slack teams (share a channel). Another common use case is federation between a group in Skype and a channel on Slack. Or IRC and Telegram, etc. Making existing systems work together really well is priority one. API only makes sense once that's done.