ry755 has ported the open source emulator uzebox to the nintendo 3ds
How to setup the emulator and load games:
Download the latest release from the GitHub repo: https://github.com/ry755/cuzebox3DS/releases
Extract the cuzebox3ds folder to /3ds on the SD card (it must be in /3ds/cuzebox3ds)
Copy any downloaded .uze games to the cuzebox3ds folder (it must be a .uze file, .hex files won't work)
Start cuzebox3DS using the Homebrew Launcher, and after a few seconds you should see a menu called "UzeBox Game Loader"
Use the D-Pad to select a game, and press Start to launch it
To return back to the Game Loader, simultaneously press and hold Y+B+Start+Select. (a few older games, such as Pacman, don't respond to that combo)
To quit cuzebox3DS and return to the Homebrew Launcher, press ZR
If there is only one .uze file in /3ds/cuzebox3ds, it will automatically load that game instead of showing the menu.