Raspberry Pi 4 is a low cost single-board computer which has powerful Broadcom CPU and choice of RAM. With the Pi 4 you can build a low-cost PC, smart home devices, a game emulation machine, stream 4K videos and an even faster networking at the comfort of your own home with a low cost. It's a powerful platform for building your own hardware and software. The GPIO ports allow you to extend the device with your own and third-party hardware, usually referred to as HATs (Hardware Attached on Top). You can start with Raspberry Pi's own Raspberry Pi OS, a custom version of Debian, that comes preconfigured with basic programming tools and a list of recommended educational and programming tools.