Are abandonware games legal?
Not all the games on Abandonware DOS are available to download. A game tagged "NOT abandonware" is, simply put, a game still on the market, hence "not abandoned".
Abandonware is a strange definition. Abandoned games are not really free; the original developers (or publishers) ceased to exist or doesn't care anymore. Some old games were never released for free (or "liberated") and some of the early software companies are still in business and want to protect in some way their intellectual property.
I try to pay attention to online publishers in order to avoid uploading games still sold somewhere in a way or the other. It happened more than once that someone kindly (or not) wrote to me asking to remove a game from AbandonwareDOS and I always promptly complied.