'I think I may have somehow missed the end of the world... (various parts)'
The Key Program appears to be a software component of a larger mechanism capable of affecting the structure of a given universe. Described as dangerous but unable to crack the wall of a reality on its own by Noah Fulmer. The Key Program also appears to be a sentient piece of technology, created through a Brownshirt volunteer who permanently modified his own form in order to perform a very specific task related to the shield structure. He has previously known and worked with Heath (although Heath doesn't remember), describing him as 'Helpful Human Heath'.
The Key Program will perform his task when taken to the main Capital Temple. Little else is known of the nature of the Key Program, other than it being collected by Noah Fulmer based on information provided by Heath, and initially stored on his phone.