Syn68K is the “synthetic” CPU that powers ARDI's emulator Executor.
The documentation provided with Executor describes it this way:
“Syn68k is the name of the synthetic CPU that Executor 2 uses. Syn68k is both highly portable and fast. The portable core of Syn68k, which works by dynamically compiling 680×0 code into an efficient interpreted form, was designed to run on all major CPU's. On supported architectures, Syn68k can also translate 680×0 code into native code that the host processor can run directly.”
In October of 2008, the source code of Syn68K was released to the public.