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The source code is hosted on Bitbucket. You can download ('check out') a copy of the code with the following command, as long as you have git installed:
git clone https://bitbucket.org/jwaagen/openarchaeosurvey.git
You can also download the server install script here (use save as... to save the file, rename it to server_install.sh, make it executable and run it).
Go to the source code for the plugin on Bitbucket