This is the first release of the Geo AR Toolkit (GART). The zip file attached includes GART.dll which you need to add as a reference to your project. You will also need to add a reference to Microsoft.Phone.Controls.Maps.dll
which can be found in Program Files\Microsoft SDKs\Windows Phone\v7.1\Libraries\Silverlight
Please see the Documentation
tab for information on how to get started with GART.