The modules you request have different focuses. In short words:
PPC: Completely FOCAL with Synthetics, various apps, like plotting, root finding, etc, and many utility fcns (mosty synthetic)
ZENROM: Completely in ML. Targeted at the ML and synthetic programmer.
CCD: Completely in ML. Targeted at the programmer _and_ the user. Unique user interface extensions (CAT,ASN,XEQ, direct synthetics), I/O fcns, PEEK/POKE, Matrix fcns, and much more.
You could take a look at the appriorate user manuals at TOS to compare the features in detail.
My favourite is the CCD module, and the CCD OS/X (of course;-)
HTH
Raymond