MedStack reduces the time and cost to build integrated patient-centric healthcare apps by 60%. We specifically address, through a series of secure cloud tools, the biggest challenges faced by healthcare app developers: data integration and privacy compliance. Our toolset features a compliant standards-oriented cloud database, healthcare workflow building blocks for identity, data acquisition, storage and messaging, and a unified data model based on Apple HealthKit / CareKit and HL7 FHIR that significantly simplifies healthcare system integration.