OpenORB provides a Java implementation of the OMG CORBA 2.4.2 specification. So can be used as a programming library of a series of services.

Along with the ORB, the following OMG Services are provided:

Concurrency Control Service
Event Service
Interoperable Naming Service
Notification Service
Persistent State Service
Property Service
Time Service
Trading Service
Transaction Service
for Installing it in unix, ask a linux  forum which system files must be modified to install a service in linux

OpenORB is an alternative to standard Java CORBA ORB.
it is in BSD like License since now Java is GPL it is not much needed now unless you need better license or latest CORBA standard.

CORBA is part of Java platform
current RMI is implemented over IIOP CORBA protocol

OpenORB has implemented CORBA version 2.4.2
Java ORB has implemented CORBA version 2.3.1

in CORBA you don't need to install a Container like J2EE, CORBA components run stand alone.
but you need to run a name server  which CORBA client and servers need it to be able to speak with each other.
the name server also don't need to be installed  since it is implemented in java but you can run it as a deamon in linux  to prevent manual startup.

do you know how to run java application in as linux  demons?

very good explanation in : http://en.wikipedia.org/wiki/CORBA
please see it.