If you have a paid game you might want to provide a demo or trial version to download for free. The demo option will appear below an uploaded file once you apply a minimum price to the project. Just enable it and click save. The option is labeled This file is a demo and can be downloaded for free.
Demos will appear on a separate section below the purchase area on your games page. Visitors can download the file instantly without having go through any additional steps like create an account: