Well, basically those are games that exists long ago, and either the publisher and things no longer exist, or the situation is so embigous and lost thru time that no one can claim it. There are also things that the original company would release it for free since th games are so old and you can't really sell it now.
Eitherway it is basically things that no one supports, and no one cares.
It is fun games really, but it is sometimes also sad. Some of those publishers were one great game companies, and they are no more. For an old fart like me, its like reliving lost time of my childhood or something.