Quite so. I meant "PGP" in its generic sense, which includes everything derived from Phil Zimmerman's work in the 90's. PGP Corporation is only one such (commercial) vendor.
I use GnuPG on my Mac, Linux, and Unix systems. I use PGP Corp's products on my Windows and Mac systems. They all play pretty nice together.
I find that GnuPG's OpenPGP integration with Mozilla Thunderbird for email is far superior to any of PGP Corp's email-savvy products, but that's just my own experience.