This is page is about licensed games that have interesting emulators in them that were exploited to play other games not originally intended.
Sega Smash Pack Volume 1Edit
This was a compilation of Genesis games for the Dreamcast. It featured a Genesis emulator and a plain-text document on how to use it. You can read the full story about it here.
Download: Sega Smash Pack - Echelon
In 007 GoldenEye for N64, there is a fully-functioning ZX Spectrum 48x emulator that nobody knew about until 2012. The game also has 10 ROMs in it too, all of which were made by RARE. You can read more about it here.
Download: Patch (Replace with pre-patched verion if you can)
This is a game for GameCube that contained a emulator for playing Pokemon Mini games. Hackers removed the emulator to make a stand-alone Pokemon Mini emulator for GameCube, and because of their efforts later Pokemon Mini emulators were made by reverse engineering it.
Download: SHizZLE's Pokemon Mini Emulator