Libretro is a simple but powerful development interface that allows for the
easy creation of emulators, games and multimedia applications that can plug
straight into any libretro-compatible frontend. This development interface is
open to others so that they can run these pluggable emulator and game cores
also in their own programs or devices.

Nestopia is a portable and cycle-accurate NES (Nintendo Entertainment System)
and Famicom emulator written in C++. Nestopia UE (Undead Edition) is a fork
of the original source code, with enhancements from members of the emulation
community. This includes support for new platforms, and bug fixes in the
emulator core.

It can emulate a Famicom Disk System, which requires the DISKSYS.ROM BIOS file
to be placed in the RetroArch system directory or content directory.