From the official site: Neon64 is a Nintendo Entertainment System emulator for the Nintendo 64, written in MIPS R4000 assembly by Halley's Comet Software and assembled with U64ASM, our own R4000 assembler. It can be run on the N64 by using a backup device, such as a v64jr. It is also the first program of any kind that can be run on the N64 with a Gameshark Pro.
Last version released on 06/01/04:
The Wizards & Warriors bugs go away when I shrink the graphics cache by half, and the games that need a large cache for speed (Battle Tank, TMNT2 and 3, Xenophobe) all seem to run fine. So here's version 1.2a, with source.