[skyfaller]

I like LimeChat http://limechat.net/mac/ for an open source app, it's been somewhat dormant but it got an update semi-recently.

Textual https://www.codeux.com/textual/ is a proprietary paid app that seems to be under more active development. I used it for a bit and enjoyed it, but prefer FOSS when possible and switched back to LimeChat when it got updated again.

[andrewjanke]

LimeChat is great. I use their mobile version, and it is about the fastest iOS app I've ever used.

I'm still Textual on the desktop, though.