Emus for 3DS currently contains a single core VirtuaNES for 3DS, a high compatibility NES emulator for your old 3DS or 2DS. It's not as accurate as FCEUX or Nestopia, but it runs at full 60 FPS for almost all games, and supports tonnes of mappers: MMC1,3,5,6; VRC1,2,3,4,6,7; and tonnes of other mappers. As a result, the library of games it supports are huge.
This 3DS version also fixes a few bugs from VirtuaNES's MMC5 mappers and even plays Rockman 4 Minus Infinity and Zelda Legend of Link hacks.
It also runs on your New 3DS as well!