German Federal Police uses open source XMPP client 'Conversations' internally

XMPP is huge for law enforcement and military applications. In fact XMPP is successful enough to keep updating the standard because of its penetration in that market -- even though it can't seem to make a difference in the "messenger of the day" market where it seems there was AIM, ICQ, Paltalk, Paypal, Google Chat, and Facebook Messenger which share some characteristics: (i) they don't improve over time, (ii) they don't interoperate and (iii) you will be using something else five years from now.

It is quite easy to encrypt a jabber or a similar server. My inner circle of friends still uses one. You can have transports to some other forms of social networks if you want to.

Compared to modern social networks thinks like IRC and private IM-Servers look like the future again. Yes, it is more exclusive most of the time, but just so much better.