Mahout is always looking for contributions, especially in the areas of documentation. See our How to contribute page for details.
The source files are stored using Git, our page on version control has details on how to access the sourcecode.
Javadoc and Scaladoc documentation is available online by module:
Mahout is continuously built on an hourly basis on the Apache Jenkins build system.
Every three months Mahout submits a report to the Apache board. All of the drafts that get sent are checked into svn. See here: