It’s helpful to think of Cardstack “environments” rather than "apps." Although Cardstack is built for the web and not native, in some ways its mental model is more similar to an operating system than a web app. For example, say you make a Word doc, and then share it with someone else, who then makes revisions and sends it back to you via email. That’s analogous to a developer authoring a Card, making it available for others to use, and accepting revisions. Someone could build an app using Cardstack, but Cardstack itself is not an app.