Just one. The one complete and open system for the 3%. SnakeOil 2000.
Seriously, though (Ha!), Solaris, AIX, Digital Unix, Irix, HP-UX, Linux, FreeBSD,
NetBSD. And practically anything which is XPG-compliant, like OpenVMS. Source
code distribution's the easiest, IMDO.
"The wit and mind of man, if it work upon the matter, worketh according to the
stuff and is limited thereby. But if it work upon itself, as the spider worketh
his web, then it is endless and bringeth forth indeed cobwebs of learning,
admirable for the fineness of thread and work, but of no substance or profit."