Emulators on 3DS
Since the 3DS homebrew exploit, provided you can do this exploit, you can install a variety of emulators taking advantage of the hardware.
- GameYob: GB/GBC emulation.
Game Boy Advance
The 3DS does include natively a firmware for a GBA mode, used for the ambassador releases. But its compatibility is a hit and a miss, missing features, and its software mode actually runs very slow.
Some homebrew apps do real GBA emulation on the 3DS:
Some have tried injecting alternate ROMs in the available Virtual Console releases (MD, GG, NES, GBA Ambassador, GBC, Japanese emulated SFC compilations) with varying degrees of success. VC emulators for Sega systems in particular have high compatibility.