The source can be checked out anonymously from SVN with the following command:
$ svn checkout http://svn.apache.org/repos/asf/incubator/ambari/trunk ambari
You can follow all the work going on by watching the Ambari JIRA project. You can see the JIRA details for Ambari 1.3.0 here:
Take a look at how to install a Hadoop cluster using Ambari 1.2.2.
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