Description: Digital platform ecosystems have become central to corporate strategy, yet existing literature offers limited guidance on how to structure multi-product portfolios in care-driven industries, that is, sectors where user engagement is shaped by emotional attachment, long-term responsibility, and variable need frequency. This paper introduces the Engagement-Frequency Architecture (EFA), a conceptual framework for organizing digital product ecosystems along a frequency spectrum ranging from daily habitual engagement to episodic, need-triggered interactions. Drawing on platform ecosystem theory (Parker et al., 2016; Jacobides et al., 2018), behavioral design literature (Eyal, 2014; Fogg, 2009), and the authorâE™s direct experience building a pet care ecosystem at a Fortune 500 corporation, EFA proposes two original constructs: the Frequency Spectrum Model, which maps product positioning by interaction cadence, and the Trust Entry Point, which identifies the acquisition layer that establishes relational credibility before monetization. The framework is illustrated through a pet care industry case where five digital products were organized across daily content, monthly subscription, periodic insurance, and episodic telehealth layers. Implications for product managers, ecosystem architects, and researchers studying vertical platform strategy are discussed.