Matrix.org is a project to create a protocol and server implementation to replace IRC.
Unlike closed tools like Slack, or even open Slack clones like Rocket.chat, Matrix is not focused on a web-client only, but on the protocol to cover all types of clients (text, desktop, web), it is federated (no single server), and it covers good IRC integration (the public matrix server is even on Freenode), and it adds features that Slack clones have like persistent history, pictures, etc.
Play with Matrix.org as replacement for IRC
