Waterhouse wrote an Arc interpreter on top of Arc with continuations, and first-class macros and first-class special forms. Scanning over his submission form (http://lispinsummerprojects.org/static/summer/250119.pdf), it also interestingly lets quasiquote be defined as a macro.
Well, since you ask. :-) And since the judging is all done, I might as well update it. So. Currently things are broken up into "dyn-cont", which has the Arc interpreter, "arc-boot", which is the code the interpreter will run on startup, and "memory-system", which is where I'm prototyping the stuff the next version of "dyn-cont" will run on: fake assembly code, which is a preparation for writing real assembly code.
