Forge Passport is SerraForge's list of available destinations. The site distinguishes destinations by development or availability state, including beta, live and active legacy worlds.
Linking a world
A supported destination may let you verify that you already own an account there. The Passport page explains the available connection method for each world. Not every destination uses the same verification system or has automatic linking enabled.
Important security note
Use only the official connection flow offered on the Passport or destination page. If a world has a manual connection process, follow that process; don't assume it immediately connects all gameplay data.