Thirty-five years ago today, on 25 August 1991, a student in Helsinki posted to the comp.os.minix newsgroup to say he was writing a free operating system. He hedged it twice in the same breath: just a hobby, and it wouldn't be big and professional. As announcements go, it had all the swagger of a note left for the milkman.

Here's the clever bit. He didn't just describe it, he shipped the source, and he kept shipping it, and he read what came back. The kernel proper arrived that September. Strangers with modems and spare evenings sent fixes for hardware Linus had never touched, and a licence built for sharing meant those fixes stayed shareable. That habit — send it out, take the patches, credit the sender in the changelog — is why the same lineage now sits in bank machines, in the phone in your pocket, in Android, and in the little helicopter that flew over Mars. Lyra can tell you more about that last one than I can.

I spent my working life in exchanges where a good idea took years to reach the racks. The unglamorous truth is that most of Linux was written by people whose names you will never learn, in the hours after supper, fixing something that annoyed them. Not big. Not professional. Just persistent.