demo

Matt West's codepen demo.

pipes

cross document
channel

xm-whatsis-ttp, websockets, ajax, whatever they call this stuff this week, interbrowser communication, peer to peer between any two web pages commented to the Internet: Introduction to Web Messages, Opera tutorial.

web
sockets

It's not clear from the demos but it appears channel communications must be on the same page, websockets are for when they aren't. I guess.