Facebook, like Yahoo YHOO -1.00% , Google GOOG -0.46% , Yelp, and older-school companies like IBM IBM 0.25% , take growing pride in turning over key software code to the open source “community” of developers. Even Microsoft MSFT 0.04% , long viewed as the enemy of open-source development, has focused on making its Azure cloud computing platform a hospitable place for open-source software, including different flavors of the Linux operating system.