* Standard text messaging app, for almost everyone.
* Google Hangouts, which is a pain to remove and always logs in behind my back. I don't want to chat on my phone, it's just a nuisance. (I wish people would stop talking to me through Hangouts, honestly)
* Viber, with a single contact.
* LINE, with a single contact.
I don't have WhatsApp or Snapchat or whatever, but most people will likely have 3 or more messaging apps.
3 years ago, everything was fine. Google used XMPP. Facebook used XMPP. Companies used XMPP. I used XMPP. I may have needed multiple accounts, but I needed only a single app. Now look where we are.