Memory is shareable between threads but not between processes
Totally untrue. Memory is ALWAYS shared between threads, it is BY DEFAULT not shared between processes, but can be EXPLICITELY made shared betwwen processes.For this you can use either file mappings, or shared segments. From BlitzMax your best bet is to use file mappings. A file mapping (Windows specific) lets you access to a shared area in the virtual memory space. Type "createfilemapping" in google and from there you should find the needed information.
As Budman said, that's totally platform-specific.