I don't know about Discord that was given as an example earlier for a single login, but most tools allow you to have multiple emails with a single account (eg.

I don't know about Discord that was given as an example earlier for a single login, but most tools allow you to have multiple emails with a single account (eg. think Github which most of the same companies use). There is nothing stopping Slack from doing the same while still getting money from companies needing their service.