It is a cheap computer. With a monitor, keyboard and mouse you are set. The OS runs on a SD card. It has general purpose GPIO inputs and outputs hence it is easy to boot a linux OS of your choice and use the GPIO pins to control or measure things. The applications are education, home automation, thin client, media center, NAS, VPN, firewall, … . A worldwide community for answering questions and a lot of people posting their projects on the web so you can reuse what they did. Did i mention that it is cheap?
Hardware and software advisor for tech startups. ASIC, FPGA, RPi, Arduino, AI, robots, drones, blockchain, Machine learning, vision processing, IoT and 3D printers are my fields of expertise.