Well, sure, you could say there are different degrees of "proprietary," but there's really only one "open":<p>1. Secret spec, patent-encumbered
2. Secret spec, patent-free
3. Open spec, patent-encumbered
4. Open spec, patent-free<p>You can of course expand that out to include other criteria, but... you get the idea.<p>I'd argue that #4 is the only one that's really "open," though a case could be made that #3 is both open and proprietary rather than simply proprietary.<p>Of course there are those who believe #4 isn't really feasible and that some patent somewhere can apply to basically everything... even if the patent holder doesn't know it.