RetroArch Debian

Install it:

$ sudo apt-get install retroarch

There are the emulators, RetroArch only is a front end.

$ sudo apt-get install libretro-nestopia

$ sudo apt-get install libretro-desmume

$ sudo apt-get install libretro-mgba

You must enable non-free repository.

$ sudo apt-get install libretro-snes9x

You must enable non-free repository.

$ sudo apt-get install libretro-mupen64plus

Genesis / Mega Drive, Sega/Mega CD, Master System, Game Gear & SG-1000

$ sudo apt-get install libretro-genesisplusgx

$ sudo apt-get install libretro-gambatte

I installed all of above:

There are the roms of games, RetroArch only is a front end.

I use a directory named $HOME/roms with subdirectories by console, for example for NES: $HOME/roms/nes