I've heard wonders of Lisp OSes, but haven't tried one.
There’s also Mezzano which is a relatively new, from scratch Common Lisp implementation on bare metal: https://github.com/froggey/Mezzano
Finally, if you know where to look, it’s possible to setup a Symbolics VM on Linux, which is somewhat interesting to poke around in (all the manuals available out of the box are pretty interesting to read through.)
It just seems really cumbersome and that is a shame, because it seems so worth to take a look at it.