Methods, systems and apparatus, including computer programs encoded on a computer storage medium, for receiving an application installation log, the application installation log including per-user installation data indicating when each of a plurality of applications available through an application marketplace was installed on a plurality of computing devices, determining an overall score corresponding to a first application and a 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, and storing the index in computer-readable memory.