As far as messengers go, IRC is about as far from Slack as you can get. Two main differences: 1. You can't send IRC messages to people who are offline (yes you

As far as messengers go, IRC is about as far from Slack as you can get. Two main differences: 1. You can't send IRC messages to people who are offline (yes you can work around this with bouncers etc. but that's beside the point). You can send Slack messages to people who are offline. 2. Slack is a proprietary, centralized system. Slack, the company, decides who is allowed to participate, and at what cost. IRC is a federated protocol, where different servers can be part of the same network, or part of a different network. You can set up a server or client by yourself if you want.