Slack used to have that benefit when they had their IRC and XMPP gateways online. I know there are clients out there that leverage the API to do the same thing

Slack used to have that benefit when they had their IRC and XMPP gateways online. I know there are clients out there that leverage the API to do the same thing, but it's essentially re-inventing the wheel covered by numerous existing IRC and XMPP clients.