RPG Maker VX Ace is the engine Five Nights at F***boys was made with.
RPG Maker VX Ace is an amazing engine which lets you create RPGs easily! And they say that truthfully.It's dead easy! People say that it's for people without a programming knowledge but there is custom scripting to improve the engine at your will (not many people use custom scripting) and some people such as the creator of this topic knows code really well.
The Five Nights at F***boys ZIP Folder has a file which is the game project.If you have RPG Maker VX Ace full version you can access the project and edit it at will. Many people use it to cheat or help them make their own F***boys fan game.
It's a great engine and I recommend downloading it!