In Plan9 UNIX's ”everything is a file” philosophy is reaffirmed in a heightened and enhanced form, and all resources (CPUs, even) on a distributed network can be mounted with a simple protocol and accessed remotely. These namespaces make it possible to provide each and every program with its own namespace (to the point of being able to run a copy of the window manager within itself). For example you have /net directories with all the TCP ports in /net/tcp and those can be concatenated to forward ports or even create routers. It's amazing.