You can share memory in other ways, via mmap or SysV shared memory.
You could imagine an implementation of the Ruby interpreter which kept all the expensive and shareable state (bytcode and class metadata, i suppose) in a shared memory segment, and used spawning to create worker processes with their own process heaps, but sharing that segment.
It would be a lot of work to implement. It would probably be easier just to get Ruby to use threads properly.
