Duke is licensed on an annual basis, and this license is managed using a license key which is provided when you purchase the product or when your existing key expires. The license controls which features of the application are available depending on the type of license you have purchased; some of the extended features such as PowerBI integration are available only with the Extended License.
The application will notify you when the license approaches its' expiry date, the first notification being displayed 28 days prior to expiration.
The application and an evaluation license key can be downloaded from this site. However, please be aware that when running in evaluation mode, the data capture component (the part of the application that retrieves data from SharePoint) will retrieve approximately 50% of the site content. To perform a full analysis of your SharePoint environment, please purchase the full product.