Every so often, someone suggests writing an OperatingSystem to recreate the Symbolics LispMachine OS. Sometimes the projects leave traces for future generations to pick over.
Other Lisp Machine operating systems are from Xerox (InterLisp D) and TI (Explorer).
Christopher Browne's web pages include a list: http://linuxfinances.info/info/lisposes.html
As pointed out on that page, MzScheme can already run on bare hardware. See http://www.cs.rice.edu/CS/PLT/packages/mzscheme/ . From that page:
MzScheme is available in kernel form for x86 machines, which allows MzScheme to boot without the aid of a separate operating system. The MzScheme kernel is based on the OsKit.
There is also movitz, see http://common-lisp.net/project/movitz/