I use a GUI, selfhosted and web based instance of The Lounge. Ive been using it for a few years now and its wonderfull. I can be connected at all times without leaving my laptop on. Before that i used Hexchat, dIRC (was a wonderful client for windows, so mist have been around 2000) and mIRC, which i think is still one of the biggest clients.

I use The Lounge, it's a self hosted server/bouncer that you use through a web UI. That makes it so I can stay online 24/7, and can access IRC from any device including my phone. It even supports push notifications, so when someone pings me on IRC, I get notified on my phone and can go open up the client and look at my chats. It's pretty good!

Not as lightweight as a terminal client, but keeping a Firefox tab open for it isn't that memory hungry. Negligible when you have dozens of tabs open and a few Electron apps anyway.

Circe, because why would you ever want to leave Emacs