torkel104: Also, games that are only available for DRM'd platforms (such as windows or mac os) have DRM-by-proxy and cannot be advertised as "DRM-free"
Not sure about Mac programs themselves, but there are emulators/compatibility layers for Windows programs on Linux and Mac.
And I think the situation is similar with consoles, whose main objective is to be a fancy DRM, but that have programs sold as ROMs and that can be played without the validation of the original device (and when they require the original system files, some times you can get official dumps from the company, also without the needing of validating the files).