Amazing. Still boggles my mind that these huge companies can't invest in native development. You never really understand how constrained Slack is once you see what multi-window setups could look like. The current UI is mess and this is a great solution.
When I try to sign in, there is a threatening banner "This app hasn’t been reviewed or approved by Slack. Learn more." But nothing happens when I click on "Learn more". I decided to quit then. :(