Yes

Gajim and Dino are both pretty good depending on what you need and what you like. I use Gajim. On mobile check out https://f-droid.org/en/packages/com.cheogram.android/

One of those strange phenomena: people who love capitalism but hate debt.

What platforms?

Facebook never federated chat. They did federate messages via email a loong time ago, but never chat. Google did.