Modern computing is too complex for young learners to get a feel for programming. Even to write Ruby, beginners must first learn, such as managing an OS, setting up an editor, and installing Ruby runtimes. This noise makes it hard to reach the essence of programming.

In this talk, I will demonstrate how a standalone Ruby computer was built with mruby. This $20 handmade single board computer provides a complete programming environment with display output and keyboard input, all without a host PC.

I will dive into the implementation of its graphics engine featuring real-time 640x480 output and text/shape rendering, as well as a Ruby shell with USB keyboard input and serial communication with external R2P2 devices. By showing how every component runs on the mruby VM, I will demonstrate that it is powerful enough to build a complete computing experience from scratch on a tiny microcontroller.