The irony may be that it has done this by making it easy to do the one thing many people thought would kill open source, more easy: forking. I remember talking to friends who – before Github launched – felt that forking, while a necessary check on any project, was also its biggest threat and so needed to be managed carefully.
Today, nothing could feel further from the truth. By collapsing the transaction costs around forking Github hasn’t killed open source. It has saved it.