It solved usability for group chat, being much better than IRC. Other messengers solved user status, message formatting, attachments but without groups, and for

It solved usability for group chat, being much better than IRC. Other messengers solved user status, message formatting, attachments but without groups, and for personal use. Slack simply brought these features to companies. It also created consistent clients for multiple platforms, something not yet common. I was in mIRC for years before, and my company had our own channel on freenode, as did some other tangential companies and OSS projects, but we couldn’t get some less technical people to use those and they didn’t feel confident in privacy on IRC. Slack solved all that: pretty, private group chat anyone can use.