Hangouts also provides information about whether your messages were viewed and syncs chat history across devices whether they were online at the time the message was sent or not.
Message Receipt Notification is XEP-0184 and supported in most clients, though I don’t know how it works in MUCs.
XMPP also has a spec for server-side history storage, that allows for syncing to clients. I don’t know how well it is supported in reality, but understand that there are at least ejabberd modules for the server-side part and a plugin for Pidgin to view this stored history. Not perfect, yet.
I don't care much about receipt notification but chat history sync was probably one of my biggest annoyances with GTalk. I'm glad to see it solved in some way although it is disappointing that Hangouts doesn't support XMPP anymore.
Well, it is being addressed. Ideally, I would like my phone to tell the server to save history of its chats, Pidgin on the desktop syncing these chats over from the server and then deleting them from the server and the server making sure that, if Pidgin is running, it gets messages instantly even if they are sent to/from the phone, either by pushing Pidgin to sync history or ignoring the full JID and always doing a CC to Pidgin.
I guess it is a long way till we get there, though :|
XMPP also has a spec for server-side history storage, that allows for syncing to clients. I don’t know how well it is supported in reality, but understand that there are at least ejabberd modules for the server-side part and a plugin for Pidgin to view this stored history. Not perfect, yet.