Our games are built from the ground up, all new code (6502 Assembly), and all new parts for the cartridges. There's no specific engine for NES games but there are tools out there if you're interested.
It depends what you're working on. For instace, for graphics, these are two popular options:
NEXXT - https://frankengraphics.itch.io/nexxt
NES Screen Tool - https://shiru.untergrund.net/software.shtml
Check out this page for a thorough list - https://www.nesdev.org/wiki/Tools