Please don't use Slack for FOSS projects (2015)
Acting like IRC is equal in functionality to Slack or Discord is straight up delusional.One of the biggest problems with IRC is that there is no immediately obvious way to jump into a channel and browse or search the history.Also, because there are so many IRC clients, and so many 
servers out there, one person's IRC experience can vastly differ from another's.IRC also doesn't have any of the modern amenities like emoji reactions or reaction gifs, comment threads, code snippets, plug-and-play third party integrations and web hooks, profile pictures, voice/video chat, screen sharing, or any number of a plethora of other features that BOTH Slack and Discord have.If you want people to use an open source alternative to Slack or Discord, then people need to build that alternative. IRC, unfortunately, is not it (at least not in its current aged state).