WINE is an
attempt to
reimplement the
Windows API on a
Unix-like
platform. I'm not sure what
license it's
under, but it goes along with
free software and
opensource concepts, I'm sure. If not
LGPL then probably
BSD-type.
Although it
stands for "WINE Is Not an
Emulator", that is
debatable. From a
technical point of view, it is not
emulation because all
code and
hardware access is done 100%
natively. But it really does have
emulator-like
functionality, and could be
considered an
emulator by some.