If you go to that URL, you'll see the landing page for the atproto PDS software.
Edit: Ah, and seems Kuba is hosting a directory of profiles using their own PDS as well, lots of examples over there: https://blue.mackuba.eu/directory/pdses
Biggest one right now (excluding the default one) seems to be atproto.brid.gy, which has 40393 accounts.
One example of a profile that lives on a different PDS ("AT Protocol Personal Data Server") than the default one: https://bsky.app/profile/mackuba.eu
If you look in the bottom left of https://clearsky.app/mackuba.eu/history, it shows:
> User changed [...] 1/2/2025 to external server PDS: https://lab.martianbase.net
If you go to that URL, you'll see the landing page for the atproto PDS software.
Edit: Ah, and seems Kuba is hosting a directory of profiles using their own PDS as well, lots of examples over there: https://blue.mackuba.eu/directory/pdses
Biggest one right now (excluding the default one) seems to be atproto.brid.gy, which has 40393 accounts.