Source: Coda. A doc as powerful as an app.

Coda is an online document and app creator that is free. Apps created with
Coda look like a regular document, but with interactive features.

To get an idea on what is possible, check out the templates page. A Google account is required to sign in and use Coda. Coda documents can be shared with others with the same permissions that would be available from a Google Doc: View Only, Comment, or Edit. The advantage of Coda is the interactivity features.