The standard ruby distribution comes with remote object handling stuff, DistributedRuby.
On top of that, there is a TupleSpace system named Rinda.
Then there is this final layer named Ring, which is very similar to JiniTechnology, in that it allows automagic service creation/discovery/registration.
Such a technology is useful whenever
the URI of a service is not known beforehand
the URI of a name server is not known in advance
services are periodically deleted or added from a name server
services should be notified when contacted from new clients