What Mechanisms Support IPC Over Network?

[portal!cup.portal.com!Will at apple.com]

I am interested in mechanisms in UNIX and VMS for interprocess
communication across a network between machines that run the same
operating system and machines that run different operating systems (e.g.,
communicating between some process on a VAX and a process running on a
Sun).  If someone does not want to summarize here, I would also be
interested in references to any recent articles that provide a good
overview of this topic.

Thanks,
Will