Facebook's competitive advantage doesn't come from having the best reliable streaming data store at scale, or from its software in general. Even if MySpace, Fr

Facebook's competitive advantage doesn't come from having the best reliable streaming data store at scale, or from its software in general. Even if MySpace, Friendster or Google + got their hands on the whole software stack & started running it, people would stick with Facebook. So there's no cost to open sourcing. The benefit comes from being known as technically innovative in general, and for recruiting, being known as having interesting, meaty, challenging projects to work on. The impetus usually comes from team members who want to do the work. It could be to become known for having worked on the project, or a sense of giving back to the community, or a hope that you'll get bug fixes & features from outside contributors. In my (very limited) experience, managers "passively encourage" it -- they generally don't push the team to do it, but when the team asks, they encourage it.