Welcome to the Facebook School of App Design. Here, you can use Facebook's proprietary Origami prototyping tool (which the company used to build Paper), easily snatch iOS 9 graphical user interface templates, and scroll through an archive of op-eds and how-tos penned by the social network's designers. You can even tap into a repository of hands holding phones with blank screens, for when it's time to show off imagery of your new app.
All these tools are now available in one place, to anyone, on a new Facebook site called "Design Resources." Some of it is mystifying—like why Facebook is laboring to make basic iOS icons available to the public—but most of it looks pretty useful, especially for fledging app designers. Happy prototyping.
