Hi, first post, but had to respond. :-)

Just about everything that is downloadable works on a Mac. The only things which don't are Windows EXE files -- Windows programs. But you can run those in a virtual Windows machine on a Mac, with BootCamp (free, but requires a reboot into Windows), or a program like Parallels, which is a virtual Windows machine on a Mac.

PDFs are platform independent, and most video formats work on a Mac.

If you're selling web software scripts, they only need a browser, so the platform doesn't matter.

Ditto for images, etc.

Offhand, I can't think of anything downloadable that Mac users wouldn't be able to use, aside from Windows programs -- what are you promoting?