All of the source code and documents are hosted at http://www.nitrc.org/projects/hammerwml. Click the "Download" on the left side of web-page and then you will see the drop-down box for download. Choose "hammer_itk.tar.gz" to get the source code, "HAMMER_Tutorial_V4.pdf" for the step-by-step tutorial, and "HAMMER_Doc_V4.pdf" for the implementation detail (API specification) for developer.

Use the following command to get the nightly-build source code (for HAMMER developer):
svn checkout https://www.nitrc.org/svn/hammerwml