Amongst your switches is a link exchange option. When activated, members who have links listed in your directory can trade links with other sites listed in your directory. In other words, you can run a link exchange directory.

When the switch is on, a "request link exchange" option appears to members by links which are owned by other members. When clicked, it prompts them to specify which of their own links they want to exchange with that one. When they select that, the other member is alerted and prompted to approve or deny the exchange. If they approve it, the requesting member is instructed to place the link. When the requester has placed the link and it's verified as present by the script, the other member is prompted to do their part to complete the exchange.

Note the link exchange system is for registered members, not unregistered guests, so they'll need to sign up first.

To customize text/html associated with link exchanges, look at Admin -> Customizations -> Language (search for some part of the wording you wish to change) or Admin -> Themes -> Manage Templates -> "Link Exchange Request" / "Link Exchange Jobs".