1. A system, comprising: one or more computers; and a computer-readable medium coupled to the one or more computers having instructions stored thereon which, when executed by the one or more computers, cause the one or more computers to perform operations comprising: receiving an application installation log, the application installation log comprising per-user installation data indicating when each of a plurality of applications available through an application marketplace was installed on each computing device of a plurality of computing devices; for each first application and second application of the plurality of applications: determining an overall score corresponding to the first application and the second application, the score indicating a degree of overlap in installation periods of the first application and the second application on the plurality of computing devices; determining that the overall score is greater than or equal to a threshold score; generating an index, the index associating the second application as an application of interest in view of the first application; storing the index in computer-readable memory; receiving a user selection of a particular application of the plurality of applications; retrieving one or more applications of interest based on the particular application using the generated index; and providing the one or more applications of interest for display.