I operate a web directory and made it so that other websites can install it and pull the categories and links from my database (an effortless web directory).
I recently discovered I could install it in my FaceBook account too very easily. All that someone else needs to do to get one also is to register at my site, get the script and install it on their website. Then, they build their faceBook page and pull their webpage/directory into their faceBook with the FaceBook iframe.
But I am wondering that since this system doesn't use FaceBook for any transport of data does this usage technique really constitute being an app? Technically all that FaceBook is doing is importing text from my site.