The existing literature on "two-sided markets" addresses participation externalities, but so far it has neglected pecuniary externalities between competing platforms. In this paper we build a model that incorporates both externalities. In our setup differentiated platforms compete in advertising...

For several years, an increasing number of firms are investing in Open Source Software (OSS). While improvements in such a non-excludable public good cannot be appropriated, companies can benefit indirectly in a complementary proprietary segment. We study this incentive for investment in OSS. In...