What? Slack specifically is asynchronous (unlike traditional irc). Any chat app with full history is asynchronous, even irc if one stays permanently connected to the server and messages are not missed. Do people not get that to have an asynchronous conversation, any tool will work? It's the people's perception of the conversation that needs to change. Email, chat, sms, signal, WhatsApp, Facebook, etc etc etc are all asynchronous. Hell other than voice and video chat, do you even have any examples of synchronous communication? I bet you don't. You're solving a problem that doesn't exist.