As of January 2021, you will only be able to download the Grain desktop app if you have MacOS 10.14 or later, or any version of Windows 10.
You can still use Grain without downloading the desktop app! Simply sign up for Grain and utilize the Grain web app to import recordings, create highlights, collaborate within the workspace, and share recordings with others.
For more information on the functions desktop app, see this article.
You can download the Grain desktop app here.