Glass apps are the web app backend. You push HTML cards to the user's device, by contacting Google's REST API (authenticated by OAuth on behalf of your user).

Glass apps are the web app backend. You push HTML cards to the user's device, by contacting Google's REST API (authenticated by OAuth on behalf of your user). Those cards are your app's UI. Actions on the device (acting on cards, sharing content with your app) result in REST commands to your backend. So with something like this, you don't need to care about the nitty gritty of Google's API, you just focus on your application logic.