Escape closes the blue banner for the current channel.
Shift-Escape closes that blue banner for all channels.
I went to HipChat instead but it's got its own problems. Weirdly you can choose to get notifications for all rooms you're in or none of them, but nothing in between. Very frustrating.
(That said, if I did it over again I might pick Slack over HipChat. The integrations with e.g. Github really are that much better.)
But there is an all/here distinction-- just named everyone/channel.
In HipChat, you can be in a room but you won't get notifications if people mention "@here" while you're idle. With Slack, this isn't possible; you would get email notifications for all of the rooms you're in every time "@channel" is mentioned. Furthermore, "@everyone" can only be used in the primary chat room, not others.
https://github.com/cjbarber/hipchat-alternatives/
I while back.
This move by HipChat makes me happy.
I've attempted to move over, but HipChat is far superior for my needs.