Recommendation / Marrying Up Algorithm in PHP?

[chelseah]

Is there something that has been already developed and is Open Sourced?I'd like to develop a site that is like:http://www.swap.com/What I envisage is that a USER A puts in what they have, dvd's, book's, cd's, etc. USER A then puts in what they are looking for themselves.The system then does a check against all the users. It finds that USER B is requesting items thats in USER A's inventory.So USER A can swap item X for USER B item X.I just don't want to try (operative word here being try) to reinvent the wheel if its kinda been done before.Thanks