content: Ejabberd's primary function is as an XMPP server, which is primarily text based chat, but has support for video, sharing files, multi user rooms, etc. It is fully federate-able with other peoples' XMPP servers. So as with email you can talk to people from other domains. Facebook's chat, Google's chat, and I think Whatsapp were all originally based on XMPP derivatives. Google used to even do federation with other domains. That's one of the ways they built their userbase, and then they shut it down... Check out the Conversations client on Android, Gajim on PC, and get fucked on iOS. With OMEMO encryption, you don't even have to trust the server operators. SIP is useful for VOIP and video calling.