IRC has probably 95% of the features slack has, is completely free and has been around since 1988. Seems like a logical comparison to make.
And we are comparing a service provider/client/protocol to something that is simply a protocol which is a bit apples to oranges.
Assuming the same kind of provider exists in your company (IRC+BNC+searchable logging) and you standardised on something like weechat, then perhaps a comparison could be made.
Slack Pros:
- Voice/Video chat
- slackbot "remind" notifications
- Number of highly polished integrations
- Rich integrations (button prompts etc)
- Webhooks for bot integrations instead of needing to subscribe to RTM
- User tags ("out of office" markers, "in meeting" markers)
IRC Pros:
- Your data doesn't have to leave your site
- You can force connections to be on your intra-net
- Simple, well understood protocol
- Which is open, and not going away
- More potential to integrate authentication with your normal authentication provider.
- Rich moderation story
- Flexibility of client, even if we take weechat as the standard it's still possible to run another.
Is this fair? Maybe we should weight how much they're worth.
But for sure if IRC had the investment slack had then it wouldn't be "trash", there's work to bring it into 2019 too[0]
[0]: https://ircv3.net
One massive one being keeping history. Another is not being limited to text only, something people absolutely expect in this day and age.