Riot Games uses XMPP to serve chat and presence in League of Legends: http://highscalability.com/blog/2014/10/13/how-league-of-legends-scaled-chat-to-70-million

Riot Games uses XMPP to serve chat and presence in League of Legends: http://highscalability.com/blog/2014/10/13/how-league-of-legends-scaled-chat-to-70-million-players-it-t.html http://highscalability.com/blog/2014/10/13/how-league-of-leg.... although there has been internal changes is still compatible from the outside, so any client can be used.