Raspberry Pi is a series of small single-board computers developed in the United Kingdom by the Raspberry Pi Foundation in association with Broadcom. The first release was in February 2012.
The newest Raspberry Pi 4 uses a 1.5GHz 64-bit quad-core Arm Cortex-A72 CPU, with three RAM options: 2GB, 4GB, 8GB.
It has gigabit Ethernet, integrated 802.11 ac/n wireless LAN, Bluetooth 5.0, two USB 2 ports, two USB 3 ports, 2 micro HDMI for dual displays 4K output, 40 pin General Purpose Input/Output which can be controlled by software program and micro SD card slot to put operating system.
The Pi official operating system is Raspbian OS, but it can run some other Ubuntu versions, and even Windows 10. It is great for home, education and industry applications.
Raspberry Pi 400 version is a complete Raspberry Pi 4-based personal computer, integrated into a keyboard with the price of only 70€.
Many different software is available to run on Raspberry, from office suite like Libreoffice, to Python, a wonderful and powerful programming language. It is especially important to note that Wolfram Language & Mathematica are free on all Raspberry Pi.
Its computing power has enabled the creation of many projects around the world.
I am really impressed and motivated to use it as a hobby.