How is this different than wrapping the slack website with Fluid.app?
Also,
https://github.com/frankdilo/sblack says "Sblack is no longer available for download since the app is in violation of the Slack Acceptable Use Policy. It was fun while it lasted, sorry guys!"
Also, telling me that it's safe without any evidence is awful. Don't do that. Link to the github repo instead of these meaningless "I promise that you can trust me, honest!" shenanigans.
Also, forcing an email signup to download? HAHAHAHAHA.