LispOS Project - Goal: reflective OS based on LISP. Mostly merged with TUNES. No code, but many ideas politely presented in a fascinating archived mail list. Mail list archives.
TUNES Project - Open source resource for learning about programming languages and operating systems. Led by French OS philosopher Fare'. Some 2,000 links.
Ultra Programming Language Project - Goal: create an advanced open source language and compiler. Interesting mail archives. Allied with TUNES.
UniOS: A Concept OS - Merging with TUNES. Some useful ideas with very clear, well written explanations, and links. No code.