It might be unclear who even owns the copyright to some of these games, as such things are lost in the shuffle of mergers, acquisitions, bankruptcies, and closures. There are, however, plenty of old games that are classified as abandonware, software that is no longer sold or supported. Unfortunately, GOG.com doesn’t have everything yet (come on guys, how about some Ultima or System Shock!).
I’ve professed my love of GOG.com in the past for buying older games that will work on your new machines, and come with all sorts extras like manuals, wallpaper, music, and so on. A few weeks ago I mentioned the Boxer DOS emulator for Mac webpage and how nicely the program worked with old DOS games.