I did not analyze exactly how it would be written, but it would be an easy script. As far as I know, Page Rank is no longer updated / (used), but the program could pull some other information about the websites, could be something like numbers from
OpenSiteExplorer.org,
Majestic.com, or
ahrefs.com.
Links would need to be added by hand, I think, and it could be anywhere on the domain, to make it easier. I am not sure how this part would work. I guess nobody would be adding all blog posts urls of 100 or 200 blogs that they have to the program... Again, Linkspun.com works, Links Organizer used to work, something like this should work too.
Links Organizer screenshot
Maybe people from
Smart Scripts could look into something like this. They have not released anything for quite some time. It would be good if it would be done by one of the good companies, and it would be supported / updated, and so on...
It can be started as something simple, then expanded, I am not sure...
# # # Edit:
People could be requesting a trade on a certain page too http://domain-name.com/page-name-here, and they would be placing their reciprocal link on one of the pages of their site too, so this could be anything... It would not need to be all in the system, people could choose, and request it. Again, I am not sure exactly how this would work.