The goal of this clinical trial is to test the efficacy of a mobile app, Combine, to increase the uptake of HIV and STI testing and pre-exposure prophylaxis (PrEP) over 24 months and to assess the effects of different implementation strategies on intervention maintenance among GBMSM in rural southern United States. The main aims of the study are: * To assess the relative effects of three treatment conditions on gains in engagement in HIV prevention compared to a modified standard of care control condition * Measure and assess secondary factors affecting app implementation * Refine implementation strategies and coordinate with potential funders Participants will download an HIV prevention smartphone app and be randomly assigned to one of four groups: * Control: App access only * Self-testing: App access + ability to order HIV and STI self-test kits * Motivational interview: App access + motivational interview to develop plans to use app effectively. * Self-testing + motivational interview: App access + ability to order HIV and STI self-test kits + motivational interview to develop plans to use app effectively. Researchers will compare each of the latter three groups to the control condition to see if HIV and STI testing increase in these groups