When Slack still had the IRC bridge, I participated in my company's team slack using Irssi. There were a few things that didn't work great, but it was so snappy compared to the official client and I could run it in a tmux alongside everything else I was doing (I was in a devOPS role; light on dev, heavy on ops). Plus it didn't fill my screen with animated gifs all the time... that was nice.

There's still a community I hang out with on IRC, and I started thinking about finding an IRC client for my new Macbook Pro (have been using X-Chat on Linux for months). Just the other day on HN I learned about Erc, which is an IRC client that's built right into Emacs. Tried it out last night and it's working awesome so far! Now if only the 8 Slack teams I'm a part of would switch over...