It's funny to see 3rd party integrations listed when IRC was barely more than telnet and was stupid simple to interact with programmatically. I wrote my first IRC bot, from zero knowledge to functioning in the channel, in 45 minutes. Try to do THAT with the Slack Integrations API or whatever. And that was when I was still learning how to code!
- history (this is probably the biggest)
- in-line replies
- 3rd party integrations
- gif/photos/files