Thanks Hawk!

Dungeon Keeper is not abandonware so you will have to purchase it. You can find it at a lot of places, especially online game stores. It was a unique game of its time because you are playing as the "bad guys" i.e. demons and imps and are trying to create a dungeon to defeat Heroes and other dungeon keepers.

the Home of the Underdogs is probably has one of the largest selections of games that are now offered as abandonware and can be downloaded for free. Most of them are old 16-bit games that you can get to work on DOSBox.