Midway games were available legally free for short period just like Prince of Persia and few other games.
You can even find an old version of Counter Strike 1.6 legally for free.

But I wonder why gog never tried to get Hidden and Dangerous: Deluxe here.
It is one of the best freeware I ever played.
We still have Dragonsphere as free game although it was recently in a sale.
Gog should add H&D:D soon.