If you&#x27;re trying to argue &quot;pre-built&quot; on the basis that they started with some existing code, that defines almost all software, so does not seems like a useful definition.<p>I think most commenters here would generally associate &quot;pre-built&quot; with the licensing of an existing engine available on the open market.  Such as Unity, UE4, etc.<p>The very top AAA game studio actually use their own proprietary engines.  For example, EA uses the Frostbite Engine in many titles:<p><a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;List_of_Frostbite_games" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;List_of_Frostbite_games</a><p>Even if I were to accept the strict definition you proposed, 
many of the upcoming titles on PlayStation 4, such as Dreams and Tomorrow&#x27;s Children are essentially completely new game engines.<p>They&#x27;re breaking new ground in rendering and gameplay technology and are as reasonably close to &quot;from scratch&quot; as you&#x27;re going to get at this point.