JET is only distributed as source code, since it is targeted at people that want to implement their own test suites.
Access the source code using hg clone.
The https://hg.kenai.com/hg/jet~framework URL can also be used in graphical Hg tools.
You can also get access to the project directly from NetBeans, plase follow these directions: IntegrateNetBeans
To get access to the JET JIRA issue tracker from NetBeans, you must install the NetBeans JIRA plugin.
If you want to build JET in addition to just getting the source code, please see the Build wiki page.