Ocelot
From its home page:The Ocelot project was conceived as a project to create a public-licensed implementation of an operating system similar to UNIX, but with scheme as the underlying language instead of C. It was originally an outgrowth of the old LISPOS mailing list.However, the first difficulty it ran into was the lack of a Scheme compiler appropriate for OS-level programming, device driver writing, etc. The project's focus therefore has shifted for the time being to the creation of a hardcore Scheme compiler suitable for these tasks.