Movitz
Movitz is a Common Lisp implementation that targets the x86 PC architecture "on-the-metal". Its intended use is for embedded, single-purpose systems, or operating system kernels.

You can read more about Movitz (as well as browsing the source and the mailing lists) at common-lisp.net.

The current technical documentation is available now (and 403 Forbidden).

The instructions on how to build and boot it are on the project's Trac