Here is eurosky: https://portal.eurosky.tech/
Here is blacksky: https://blacksky.app/
Here is bookhive (a lot smaller): https://bookhive.social/
I found all of them by looking through the PDS index: https://atproto.at/pdses and selecting ones with enough users to signify open registration.
Here is a guide to self-hosting: https://atproto.com/guides/self-hosting#pds
All of these are links to PDS servers. These are the servers that contain all of your data. You can log into any ATProto apps using these accounts.