"Ben Jacobsen, a model railroad hobbyist, wrote a bunch of
software to let you connect your computer to your model railroad
and control trains with it. He chose to not only give the software
away for free, but to make the source code available as well, so
that the model railroading/hacker community could improve it and
customize it to their liking.
"And then KAM Industries, maker of commercial software that
serves a similar role, tried asserting their 'patent rights' over
doing just that..."