The ultimate emulator list

Turn a Raspberry Pi into a retro gaming emulation computer !

An operating system that can be run on a USB flashdrive to turn any PC into an emulation machine ! Really awesome

THE KING !!!
You can run this on almost everything, I wouldn't be surprised if your microwave supports it. Not super user friendly but you have tons of ressources and tutorials online on how to use it.

RetroArch but with a more familiar UI (PlayStation 3 style)

The best for macOS, really user friendly and super complete !

For iOS or iPadOS I use this one since it's a WebApp you won't have problem with Apple revoking access to the app. Open it in Safari and add it to home screen.
NES, SNES, GB, GBC, GBA, SMS, and GG support.

For android this is my go to as it's user friendly and pretty complete !

A26, A78, Lynx, NES, SNES, GB, GBC, GBA, Megadrive, Mega CD, SMS, GG, N64, PSX, PSP, Arcade, NDS, PCE, NGP, NGC support.

This is a multi-system emulator but I love it for Master System, Saturn and GameGear !
Works on macOS, Windows and Linux !

The SNES

My N64 emulator of choice !

Worth mentioning : Project64

THE Gamecube and Wii emulator of choice.
For macOS, Windows, Linux and Android !

The MMJR2 version can have better performance on Android in some games https://github.com/Bankaimaster999/Dolphin-MMJR2

My go to standalone GBA emulator for macOS, Windows and Linux

The revival of the popular VisualBoyAdvance for macOS, Windows and Linux !

A really nice freemium GBA emulator for Android !

Worth mentioning :
My Boy!
John GBA

If you're on iOS, Delta is the one. You will have to download it from the AltStore !

Previously known as GBA4iOS ! It now support NDS emulation !

A nice DS emulator for macOS, Windows and Linux with an unofficial Android port !

Worth mentioning :
Drastic Android (paid)
nds4droid Android
DeSmuME dead project

The DS emulator for iOS.
NOT ON THE APP STORE, YOU'LL HAVE TO DOWNLOAD DE .IPA AND INSTALL IT WITH AltStore !