following (at present):
<dl>
<dt> <b>sunos4-sparc</b>
<dd> SunOS 4.1.x running on Sparc processors 
<dt> <b>solaris2-sparc</b> 
<dd> Solaris 2.x running on Sparc processors
<dt> <b>aix3-rs6000</b> 
<dd> AIX 3.x running on IBM RS/6000 Power processors
<dt> <b>linux-i386</b>
<dd> Linux running on Intel x86, Pentium etc. processors
<dt> <b>linux-axp</b>
<dd> Linux on DEC Alpha processors
<dt> <b>macosx</b>
<dd> OS X on Macintosh computers.
<dt> <b>cygwin</b>
<dd> Under cygwin on Windows machines.
</dl>

By def