I know at one time that there was a proprietary (licensed for fee) 
development environment that was native and portable to X11, Mac OS, and 
MS Win -- that is, using this "magic" set of libraries, etc., the same 
source code (ANSI C++ base as I recall) would have the same GUI 
interface in the developed application on all three of these.  I do not 
recall for which releases this worked.  (My assumption is that there 
must be something still like this as many "major" web browser 
applications have variants for each of these different environments.)

In a similar way, but hopefully open systems (not licensed for fee), is 
there a lowest common denominator for Linux that will work on both Red 
Hat and Debian based distros (e.g., SL, Fedora, etc., and Ubuntu, Mint, 
etc.)?  -- not necessarily the latest and greatest, but write once 
(preferably in ANSI C++ current GNU production release), compile on each 
environment, and run.   I know that this works for various interpreters 
(e.g., java, python) -- but we are looking for compiled to physical 
machine code if possible.

Yasha Karant