Other than that, IRC bots have existed for decades and already do most of what Slack integrations do.
Why does it matter if anything else does it too? Even if everything slack does is possible with irc, fact is slack is much easier to deploy at scale, much easier to get nontechnical people on, much easier to integrate with things like pagerduty or datadog.
this may just be an android thing but I had to type my gmail password into the slack app to log in with SSO. No bueno.