Frugal intelligence for circularity: A systematic review of human-in-the-Loop decision support systems in SME circular supply chain optimization

• Systematic review of 186 papers reveals only 8% integrate circular economy principles, digital technologies, and SME implementation realities, exposing profound knowledge fragmentation systematically excluding 99% of enterprises. • Conceptualizes "Frugal Intelligence" as affordable, human-centric, incremental, and collaborative decision support framework fundamentally differing from conventional Industry 4.0 approaches presuming capital availability and automation feasibility. • Operationalizes Human-in-the-Loop decision support across four circular supply chain stages (design, logistics, sorting, remanufacturing), specifying where human expertise combines with computational tools most effectively for resource-constrained SMEs. • Identifies multi-level barriers (financial, knowledge, technical, institutional) reflecting design choices rather than temporary obstacles, requiring systemic intervention through fundamentally different business models, technology designs, policy approaches, and collaborative infrastructures. • Provides integrated framework bridging Industry 5.0 principles and frugal innovation with phased transformation pathway, enabling SME circular economy participation through appropriate rather than sophisticated technological approaches. The transition to circular economy (CE) principles presents formidable challenges for Small and Medium Enterprises (SMEs) that lack the substantial financial and technological resources of large corporations. While Industry 4.0 technologies promise to enable circular supply chains, current frameworks exhibit systematic large-enterprise emphasis, effectively excluding 99% of global enterprises. This systematic literature review examines 186 peer-reviewed publications (2016–2025) to address a critical implementation gap: how can SMEs adopt circular supply chain practices using appropriate, affordable technologies? Employing PRISMA methodology and Structural Topic Modeling, we identify profound knowledge fragmentation where circular economy principles (46.8%), digital technologies (30.1%), and SME implementation realities (23.1%) develop independently with only 8% integration. We conceptualize "Frugal Intelligence “affordable, human-centric, incremental, and collaborative decision support systems that augment rather than automate SME decision-making. Our framework operationalizes Human-in-the-Loop approaches across four circular supply chain stages (design, logistics, sorting, remanufacturing), identifies multi-level barriers and enablers requiring systemic intervention, and charts transformation pathways from pilots to systemic impact. Findings challenge three dominant paradigms: circular economy literature's large-enterprise emphasis treating SME contexts as special cases, digital technology research's "proof-of-concept purgatory" emphasizing sophisticated systems inappropriate for resource-constrained settings, and implicit assumptions that barriers reflect temporary obstacles rather than design choices embedded in existing frameworks. We contribute an integrated framework bridging Industry 5.0 human-machine collaboration principles with frugal innovation, providing actionable pathways enabling SME circular economy participation previously precluded by resource constraints and advancing sustainability scholarship toward inclusive transformation encompassing organizational majorities rather than elite minorities.