For that matter, most apps written for Tiger should work on Mountain Lion, with the important exception of PowerPC apps - but that was a matter of maintaining l

For that matter, most apps written for Tiger should work on Mountain Lion, with the important exception of PowerPC apps - but that was a matter of maintaining library support for an entire architecture, and anything written for the Intel release of Tiger is fine. The other way around is different, of course, as as a huge number of new APIs have been added since then.