If you're trying to argue "pre-built" on the basis that they started with some existing code, that defines almost all software, so does not seems like a useful

If you're trying to argue "pre-built" on the basis that they started with some existing code, that defines almost all software, so does not seems like a useful definition. I think most commenters here would generally associate "pre-built" with the licensing of an existing engine available on the open market. Such as Unity, UE4, etc. The very top AAA game studio actually use their own proprietary engines. For example, EA uses the Frostbite Engine in many titles: https://en.wikipedia.org/wiki/List_of_Frostbite_games https://en.wikipedia.org/wiki/List_of_Frostbite_games Even if I were to accept the strict definition you proposed, many of the upcoming titles on PlayStation 4, such as Dreams and Tomorrow's Children are essentially completely new game engines. They're breaking new ground in rendering and gameplay technology and are as reasonably close to "from scratch" as you're going to get at this point.