Here's a breakdown:
* Official Yu-Gi-Oh! Online Games:
* Yu-Gi-Oh! Master Duel: Requires a Konami ID to play. You can sign up for a free account.
* Yu-Gi-Oh! Duel Links: Requires a Konami ID to play. You can sign up for a free account.
* Yu-Gi-Oh! Legacy of the Duelist: Requires a purchase and does not require a sign-in.
* Yu-Gi-Oh! Online (older version): This was shut down in 2015.
* Unofficial Yu-Gi-Oh! Simulators:
* YGOPro: Free and open-source, no sign-in required.
* DevPro: Free and open-source, no sign-in required.
* E-Hero Simulator: Free and open-source, no sign-in required.
In summary:
* Official Games: You need to sign in, but it's free to create an account.
* Unofficial Simulators: You can usually play without signing in.
Note: Unofficial simulators may not have all the latest cards or game mechanics.