See David Krauss's home page which links to http://uppermute.org, at last up and running (previous http://www.rebelution.net/upper/ and google's cached page seem to work no longer).

From the author: Upper is a framework for extensible modular optimizing compilers. It will allow language designers to expose the internal module interface through the language, allowing reflectivity. It's also a complete departure from traditional compiler architecture, making heavy use of object-oriented design. Mute will be the extensible programming language built to be compiled by Upper. It will be flexible enough to emulate C, C++, etc.

This page is linked from: Reflective Programming Languages