Firms involved in open source software face inherent limits on their ability to appropriate returns from technological innovation. Here I examine the business models used by IT vendors given the limited appropriability available for open source software. I show how firms capture value through complementary assets, while creating value and positive network effect through an inherent openness that attracts complementors, users and rivals to their corresponding value network. From this, I offer suggestions for future research on complementary assets and value capture in business models.