We’ve been covering Boston-based Swaptree since mid 2006. The company, which is creating a network of users who swap books, CDs, DVDs and video games, just raised a third round of financing – $3.3 million from Safeguard Scientifics. The total raised over three rounds is now $5.6 million.

To create a trade the company finds up to four users who have and want items that form a match. Then everyone prints out address forms from the site and pays the shipping (usually $2.50) to mail it directly to the next person.

One of the coolest features is the ability to enter a few items that you have that you are willing to trade – show you all of the items that you can receive for your items.

This is a model that was tried and later abandoned by the recently acquired Peerflix. Peerflix was DVD trading only, though, and charged a transaction fee. Swaptree doesn’t charge a transaction fee, and the group-trade approach that covers books, music, movies and games means lots more matches.

The company first launched a little over a year ago, and says more than 100,000 trades have been completed to date.