http://triptohell.info/moodles/junk/pourtall.pk3
might need sv_nopvs 1 still.
use impulse 10 to select the portal gun. there's also a lame grabber weapon that can pick stuff up, but no real physics engine.
very much a prototype mod.
supposedly it has some func_pressureplate entity thing, but meh, that requires maps.
source is inside the pk3.
divverent or someone associated with xonotic made some 'warpzone' library which should work in either engine if you want statically placed portals, but it can be abusive due to the qc-based traceline+movetype workarounds.
also not a single player release. :P
things can get much faster if you skip the physics parts.