Plan 9 license

[Richard Stallman]

    Perhaps the reason why the commercial software world
    is more enamored of Open Source than it is of Free Software might not
    be in the differing emphasis, but in that Open Source does
    not demand adherance to a particular philosophy.

Yes, that's it exactly.  The Free Software Movement has a particular
philosophy about freedom; this philosophy is the reason we developed
the GNU system.

The Open Source Movement has a policy of not raising this issue at
all.  This is the underlying difference between the two movements.