I had to work with open source recommendation systems and these are the ones that I found:
Duine, Apache Mahout, OpenSlopeOne, Cofi, SUGGEST and Vogoo.
More details:
Apache Mahout constitutes a Java framework in the data mining area. It has incorporated the Taste Recommender System, a collaborative engine for personalized recommendations.
Vogoo is a PHP framework that implements an collaborative filtering recommender system. It also presents a Slope-One code.
A Java version of the Collaborative Filtering method is implemented in the Cofi library. It was developed by Daniel Lemire, the creator of the Slope-One algorithms. There is also an PHP version available in Lemire's webpage.
OpenSlopeOne offers an Slope One implementation on PHP that cares about performance.
SUGGEST is a recommendation library made by George Karkys and distributed in a binary format.
I described everything I found out here on my blog:
http://girlincomputerscience.blogspot.com.br/2012/11/open-source-recommendation-systems.html
hope it helps!