Yeah it is basically the website wrapped in an app. Having it as an app makes it easier to launch, switch to (Alt-Tab), it shows up in the task list, can be pinned to one or all workspaces, this kind of thing.

I have the app installed and it is nicer due to better hotkey support, but on the other hand the Electron shell its built upon takes up far more RAM than a couple of browser tabs.

Edit: typos.

Also slack has an irc gateway so you can also use your favorite irc client like irssi.