You guys really think that enterprise-tier Fortune 500's are going to switch from Slack to a free alternative? Why would they? The money they spend on Slack isn't even a rounding error in their budgets, there's no way that they would want to cut that out and instead have their internal staff try to support some free service instead

Discord has essentially the same app but better voice/call support and other various features. But they seem focused on the gamer market.