What is medium?

I heard medium from my co-worker today. I asked him that the best place to write in English. And I come here now. I don’t know what to write right now so this is kind of test writing.

I’m working in engineering field. I write Swift/Objective-C and a little bit Ruby. Last weekend, setup Raspberry Pi for first time. Ansible is good tool to learn and make up server side environment.

I wonder how many Japanese are here?