I used ircII under various UNIXen and the resource footprint was even smaller. That being said it had a negligible UI footprint since it was a curses-based tex

I used ircII under various UNIXen and the resource footprint was even smaller. That being said it had a negligible UI footprint since it was a curses-based text UI, doesn't embed media content or render text in a GUI, and it doesn't really do much. Slack does a lot more, but it shouldn't need to burn CPU while doing nothing. But it is an illustration of how little resources you actually need for IO, simple state management and dealing with the protocol layers. You'd accept bloat in all of these areas to get more functionality, but not by orders of magnitude. Out of curiosity I downloaded ircII-latest, ran `configure` and `make`, and then started it up (about 30 seconds from clicking the link to starting the compiled binary btw). Initial memory footprint on startup was 465kB. Now it is up to a whopping 604kB. As it is mostly idling (very little chat traffic on the channel) the CPU use is at 0.0%.