I put together an app the other day with the web app builder and when I send the URL to someone it requires them to log on. The content, web map, and app are all shared publically. Also, surprisingly if I create the app using an ESRI template instead of the web app builder I am able to successfully share that app with anyone without requiring login. Is there a step I am missing with the Web App builder that will allow the finished app to be publically viewable.
I had the same question the other day. Try replacing the first part of the url to your app (which starts with your organization account) with "www.arcgis.com"
I've run across one issue with that: The disclaimer splash I created does not carry over. It's visible to those logging in to the organization version, but not to the public version (which is, frankly, the exact opposite of what I need).
I think it relates to the organization security settings. You must allow for anonymous access to your organizations website. Try this hyperlink, it may explain.....Share items—ArcGIS Online Help | ArcGIS