Raspberry Pi is the most pоpular single-board computer out there. It gives you unlimited possibilities - you can use it as a desktop computer, media center, home automation device or robotics. I am giving you yet another idea - install Linux on it and run various free and open-source command-line apps! They are fast, efficient, don't waste system resources and you can run it over SSH eliminating the need of a monitor. Of course, you can use them on every Linux powered computer, too!