Registries are mainly a list of RPC endpoints, stored into a json file and available via a web server (public or not).
You can find below a list of public registries:
-
Polkadot Network Directory Registry: The Polkadot Network Directory project is aware of many chains and projects and provides a registry that is automatically updated and based on the data available to the directory
-
SubRPC Registry: A small basic registry to get started and show an example
-
Add your registry with Pull Request