The Interim Operating System

Interim OS is a radical new operating system with a focus on minimalism. It steals conceptually from Lisp machines (language-based kernel) and Plan 9 (everything is a file system). It boots to a JITting Lisp-like REPL and offers the programmer/user the system's resources as filesystems.

You can run it on a Raspberry Pi 2, or as a hosted operating system on ARM Linux, x86 Linux, OS X, Windows, and even on AmigaOS 3.x.