It's called Plan 9.

In Plan 9, each process has its own filesystem tree, and other programs can expose themselves to this process as file servers, meaning that data internal to the programs can be accessed via the same read, write, delete, etc. calls as files. For example, when running under rio, the Plan 9 window system, the current window contents are available at /dev/window and you can write draw calls to /dev/draw to do graphics.

REST is pretty much applying Plan 9 principles to the Web and http.

You can use REST architectural principles with a faster transport and serialization. For example, using a REST style API for a messagepack or thrift RPC service.