The document discusses the Raspberry Pi, a small, inexpensive computer that can run various operating systems like Raspbian, Arch Linux, and Windows 10 IoT Core. It has 40 GPIO pins that allow users to connect external circuits and boards to control them using code. Example projects built with Raspberry Pi are described, such as a home media server, baby monitor, network-wide ad blocker, customized picture frame, automated pet feeder, and more.