Matrix is a new, open communication protocol that supports bridging with many other services. https://riot.im is the reference client, but others are starting to crop up. It’s federated, like email, so you can get an account on any homeserver and if that homeserver federates (i.e. doesn’t block communication with other homeservers), you can talk to people on other homeservers, like email.
Anyway, the largest homeserver, matrix.org, bridges all of Freenode as well as OFTC and Gimpnet, so joining IRC rooms is just as easy as joining matrix rooms. A Freenode example would be #freenode_#nixos:matrix.org.