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Artifactory http://artifactory.sf.net, is an enterprise proxy and repository manager, that is a complete new rewrite of maven-proxy. Artifactory runs out-of-the-box on a lightweight Jetty server and can also be deployed on a standard servlet container as a WAR file. It offers advanced proxying, caching and security facilities and a robust Ajax-based artifacts management platform. Documentation and full feature list are available here.
Though not yet released, Maven Archiva also provides proxy support. It is available at http://maven.apache.org/archiva/.
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