Physical computing is very fascinating and fun, but there are also difficulties that were not found in normal Ruby programming. One of the issues is its low portability. Unlike PC, some computer boards that directly uses the devices use only small microcomputer whose memory is less than 1 MB. So most of the applications work only on specific boards. If we found an interesting project, we could not try it unless I had a target board. To solve it, I propose a plan of mruby platform, consisting of a group of mrbgems that absorb incompatibilities. I talk about the project and current progress.