Psybeam
Play Pokémon FireRed together. One player runs the real game; friends join their world as guests, walking it with them, talking to its people, and battling each other and the host.
Join a game
Open the invite link or QR code the host sent you: that's all. Your browser connects straight to their game.
New guests wait in the host's Waiting Room until they're let in, unless a friend's invite brought them.
Keep it on your device
Once you've opened the game here, your browser keeps it: invite links and QR codes still open it if this site ever can't be reached. You can also install it as an app.
In your browser's menu, look for Install or Add to Home Screen.