https://github.com/raelgc/scudcloud
https://github.com/trueos/diligent
What is hilarious about this is that people made third party Slack clients which are essentially the same idea (wrapping the Slack website) but that don't consume as many resources. And these people weren't even trying. They just picked a non-stupid tool and it worked better than Electron (which is, for those who don't know, bundling almost the whole of Google Chrome only to show a web page as your application).
Interesting. In March, they've said there is no Linux Client. For this reason I've started an alternative open source client: https://github.com/raelgc/scudcloud
Aside Ubuntu and Debian, it works on Fedora, Arch, openSUSE.
I just tried it out, but I prefer scudcloud. It's got some nice keyboard shortcuts like ctrl+t
to search through chat sessions that doesnt seem to work on the official slack client.