In 2008, Microsoft hired Hamilton “Hammett” Verissimo, the founder of the open-source Castle Project, as a program manager on the Microsoft Extensibility Framework (MEF) team in the company’s Developer Division. On May 17, 2011, Verissimo quit Microsoft. People join and leave Microsoft every day. (In fact, the last of the original Xbox founders submitted his resignation from Microsoft this week.) But I was interested in hearing from Verissimo whether it was a conflict in open/closed source philosophies that led to his decision to go. It turns out many of his frustrations are similar to ones I’ve heard shared by those leaving Microsoft whether or not they were in the open-source camp.