What kind of link network are these?

Hey guys, I was checking a competitor's backlinks and found something interesting, there are lots of similar backlink pages such as:

http://www.arit.com/friends.php
http://chapter7bankruptcyinformation.net/friends.php
...

Click to expand...

They are hosted on different ips, so maybe they belong to some kind of private link networks? Or maybe there's only one person behind all these sites? Where can I find such link networks and join them?

Anybody knows?

Thanks a lot