Unless, of course, you are talking about a user-friendly service offering IRC access to those who do not want to set up their own clients.
So, something like IRCCloud, which does exist, fyi.
Rocketchat has much more feature parity to slack tbh. Comparing slack to IRC isn’t really fair even though they do the same thing.
I have used irc and slack and slack’s ease of use is its asset. I used freenode in high school and college to teach myself scheme. The barrier to entry is not something that can be explained as just use IRC.
I run an office hours chat for my online classes powered by IRC. I use KiwiIRC as the front-end.
Students need only the web address of the web page I want them to go to. When they get there, they need only a username.
No signup, no verification, none of that. They're online, getting help in seconds.
Individual public channels requiring nickserv registration and all that? that's another story.
But seriously - the barrier to entry to get started is this:
https://kiwiirc.com/client/irc.freenode.net/?##irc_can_be_ea...
Some welcome message. You may be too used to IRC to recognize this, but this is frightening gibberish to 99.99% of computer users.
Also, this interface does not get you crucial features provided by other chat services, such as seeing what previous users have said.
It's amazing to me how people think Slack is this amazing tool. If someone had thrown millions of dollars at IRC, it wouldn't suck.
But instead, you'll fork over your personal info and insist I do too.