Installing RetroArch: all old consoles in one program

RetroArch is a free program that brings dozens of emulators (“cores”) together under one roof. You install RetroArch once, download the cores for the consoles you want, and have the same controls, settings, and screen filter options everywhere.

Installation

Windows and macOS: download the stable version at retroarch.com. On Windows you unpack the zip file or use the installer; on macOS you drag the app to Applications.
Linux: easiest via Flatpak. That gives you the latest version and works on almost any distribution.
Steam Deck: via Discover in Desktop Mode, or via EmuDeck.
Android: in the Play Store.

flatpak install flathub org.libretro.RetroArch

On Debian and Ubuntu you can also use sudo apt install retroarch, but that’s usually an older version.

Downloading cores

Open Main Menu → Online Updater → Core Downloader.
Choose a core, for example Snes9x for SNES.
Then choose Load Core and Load Content to open a game.

Good cores per console

NES: Mesen or FCEUmm
SNES: Snes9x
Mega Drive and Master System: Genesis Plus GX
Game Boy Advance: mGBA
Nintendo 64: Mupen64Plus-Next
PlayStation: Beetle PSX HW
Dreamcast: Flycast
Arcade: FinalBurn Neo

Which BIOS files you need per core is listed in the Libretro documentation. Put them in the system folder of RetroArch.

Useful tips

Legal games without searching: via Online Updater → Content Downloader there are free homebrew and freeware games.
Operating the menu: the shortcut for the quick menu is F1 by default. On a controller that’s often the combination of Select and Start (or the button you set).
Controllers are usually recognized automatically. Otherwise check Settings → Input.
Sharp image: turn on Integer scaling under Video for pixel-sharp image without distortion.
Shaders like crt-geom give the look of an old TV. Download them first via Online Updater → Update Slang Shaders.
Backups: save the saves and states folders in a safe place.