J2J (Jabber-to-Jabber) is a XMPP gateway that allows to connect another XMPP accounts through it. It can be useful when you want to contact to people from some server which has no S2S support (facebook, for example) or when you want to use a second XMPP account but the client you are using can't do that.
This is a try to rewrite the original component with a twilix XMPP library, you can refer to it's description to find why there is a try to do such a remake.
Unfortunately, this remake is not yet ready to use because of a couple of reasons, but there is still a hope that it'll be ready someday.