A collection of free resources made by designers at Facebook

iOS 9 GUI (iPhone)

Photoshop and Sketch templates of GUI elements found in the public release of iOS 9

Devices

Images and Sketch files of popular devices

Diverse Device Hands

Photos of hands holding various phones, to be used in any presentation of your designs

Origami — Design Prototyping

A free tool for prototyping modern user interfaces. Get sample files and documentation to quickly build prototypes

Facebook Design on Medium

Experiences from the people designing products that billions of people use every day