If by that you mean that it doesn't require a machine with 32GB of RAM to run smoothly, then I'm all for such 90s chat tools!
Sharing files is trivial with Gist; and you get a fully proper history, ability to fork, plus works much faster than the clumsiness and memory waste that comes with Slack.
Apparently not all files that need to be shared are text files. Developers have a million ways to share text files, thank you.
(I know how to use gists to share images and other files. It's not pretty.)
It looked like hot dog vomit, but it worked wonderfully.
I have no dog in this fight as I do not use slack nor do I use irc anymore ...
However, reading this comment thread makes me think that what you all really need is neither a slack alternative nor an irc alternative ... what you all really need is a very well written irc bot.
The only useful software to get any sorts of real-time support from the community is Matrix. Nobody uses Slack in open-source simply because you can’t allow unregistered users to ask questions on public channels.
Personally, I’m a big fan of MatterMost[0] as its also open source but provides a much more Slack-like experience which new users will be immediately familiar with. You can host it yourself and it works with lots of existing integrations.
[0] - https://mattermost.com/