I work in the software business, which means that I live in a world ruled by computer code. A lot of that code is proprietary and secret. You can see what it does, but you can’t see how it works unless you work at the company that makes it.

We can, however, see some of it. A lot of the world now runs on “open source” code. That means it’s free and reusable, under the terms of its license. The Firefox web browser and the largest parts of Chrome and Safari are open source; whole operating systems, including essential parts of MacOS, are open source; the server software that powers our digital cloud, driving data to our phones, enveloping us in wonderful and terrible ways — much of that’s open source, too. If you’re reading this online, you’re almost certainly using open-source code right now.

The gates of the open-source palace are always open. You can enter by way of websites like GitHub (which is built on top of version-control software called Git, which was created by Linus Torvalds, the same person who created Linux). GitHub serves more than 100 million different code repositories. It’s owned by Microsoft, which is another sign of how things have changed: Microsoft used to write memos about how to ruin free software.

In 2019 you can track every change anyone makes to a codebase, whether they’re fixing one typo or changing 5,000 files. You can see who made the change, and read a description of the change. If something suddenly doesn’t work, you can backtrack to an earlier version and figure out why.