So yes, Jaxl can be used as a standalone server. http server (yes), xmpp server (i won't recommend).
Since both xmpp and http components are based out of same core, you can also mix and match and play, e.g. xmpp_rest
xmpp_rest example starts an xmpp client and then allow u to reach that xmpp client object via http.
Since v3.x, xmpp clients also support communication via unix sockets
(command line). So one can start an xmpp client (in the background) and then later attach to the running xmpp process. Execute (eval) arbitrary php code, Use existing xmpp client object etc. There is support for pipes
All this probably gives u endless possibilities to explore.