XQSync is a command-line, Java-based tool, useful for synchronizing MarkLogic databases to and from other databases, filesystems, and zip-files. To get started using XQSync, try the tutorial.
Note: Starting with MarkLogic 6, Marklogic Content Pump (mlcp), is a fully-supported tool that covers the same ground as this long-standing open source project. Content Pump is not supported on older versions of MarkLogic Server. Stick with xqsync if you are running earlier versions of MarkLogic.