For apps that don't quite work yet, but need a registered Stack Apps post for testing. If you're following a tutorial which asks to post a placeholder app here, that's fine, but please delete it after you're done.
In order to use the API's write access, the app's owner must have an appropriate post that is legitimately tagged with app or script.
But this is a problem for apps that are still under initial development and not ready for general use.
The placeholder tag is thus the one time we tolerate an incomplete post -- trusting that the developer will complete the post properly once the app is ready for the public.