A server system that hosts an electronic catalog of digital content items uses behavioral data to predictively select digital content items to proactively deliver to mobile devices of users. The digital content items may, for example, include mobile applications, mobile application components or add-ons, e-books, music tracks, and/or videos. An application component that runs on the mobile devices caches the proactively delivered content items in anticipation that they will be requested by the associated users. In some embodiments, the system supports off-line purchases of cached digital content items such that a user can purchase cached digital content items on the mobile device when no network connection is available.