Here are some Mac/iOS options:
LimeChat(Mac App Store): https://itunes.apple.com/us/app/limechat/id414030210?mt=12
Colloquy(Downloadable Mac): http://colloquy.info
Both are free. I use Colloquy.
iOS:
Colloquy: https://itunes.apple.com/us/app/colloquy-irc-client/id302000478?mt=8
Limechat is also available but the iOS version is $5.
There are other options as well.

To connect with Colloquy, choose "New Server", then from the Chat Server popup choose us.undernet.org or eu.undernet.org. Then you can join the chatrooms.

Debbie