What are open source's four biggest innovations, according to Riehle? If you picked "GPL vs. Apache-style licensing," well, you're only sort of wrong.
Ask someone to list a few open source innovations, and they'll likely come back with "Linux," "Kubernetes," or some other particular project. (Mea culpa.) Not Dr. Dirk Riehle, the professor of Open Source Software at the Friedrich-Alexander University Erlangen-Nürnberg. Riehle has been researching and writing about open source for well over a decade, and when he writes about open source innovations, he's thinking of more foundational elements that yield innovative code.