This review systematically synthesizes technological synergies within a Community Energy System (CES), emphasizing cold-climate contexts where heating-dominant demand profiles and strong seasonality create distinct operational challenges. Drawing on 115 studies (2010–2024), the paper explores how integrated thermal, electrical, and digital infrastructures support net-zero and climate-resilient communities in regions with substantial heating requirements. Thermal–electrical coupling emerges as a foundational mechanism in cold climates, where heating loads dominate annual energy demand and drive winter peak constraints. Power-to-Heat (P2H) systems, cold-climate heat pumps, and hybrid configurations combining Thermal Energy Storage (TES) with Battery Energy Storage Systems (BESS) enable multi-timescale flexibility, allowing renewable energy to be shifted from hours to seasons. District Energy Systems (DES) act as a thermal backbone, enabling this integration across extended heating seasons and transforming thermal demand into a grid-balancing resource. Digital technologies further enhance system coordination under variable climatic conditions. Artificial Intelligence (AI), the Internet of Things (IoT), and Advanced Metering Infrastructure (AMI) support real-time optimization, demand response, and cross-vector control within Renewable Energy Communities (RECs) and Virtual Power Plants (VPPs). At the system level, decentralized architectures—including microgrids, Non-Wire Alternatives (NWAs), and peer-to-peer (P2P) trading—strengthen resilience by maintaining thermal and electrical continuity during grid disruptions. Building on these findings, the review synthesizes cross-cutting technological synergies and proposes deployment pathways tailored to cold-climate CES, supported by comparative case studies. Despite demonstrated benefits, widespread adoption remains constrained by high upfront costs, interoperability challenges, and fragmented regulatory frameworks. The review concludes with policy, governance, and research recommendations to enable scalable, equitable, and climate-responsive CES deployment in heating-dominated regions.