As easy as pie
Grab it from the Microsoft Office Store (now called Appsource)
- You should have site collection administrators privileges to add this app.
- Sintel Forms also works on-premises with SharePoint 2013 or 2016 and in this scenario the app catalog must be configured. For more information, see How to: Set up an app catalog on SharePoint.
To add this app to your Office 365 site:
- On the site where you want to add an app, go to Settings > Add an app.
- In the navigation menu on the left select SharePoint Store.
- In the Find an app search box, paste 'Sintel Forms' and then click Search.
- Select the "Sintel Forms" app in the listing.
- In the apps details view click the button Add It.
- Follow the steps to log in with your Microsoft account to get the app.
- Click Trust It when asked to complete the deployment.
The installation will proceed and once it's completed you will see the Sintel Forms tile appear in your site.
For more information see Add an app to a site.