Which brings us to open-source code, the free software code that forms the invisible backbone to much of everything we do online. Companies like Apple and Microsoft maintain proprietary systems but baked inside are the building blocks, constructed from open-source code that is maintained by volunteers who, in theory at least, check one another’s work in a peer-review system similar to that found in science or on Wikipedia. Open-source software makes up 80 to 90 percent of any given piece of modern software.
