Heavy farm machinery such as tractors, combine harvesters, sprayers, and tillage implements represent substantial capital investments with typical utilization rates below 30% in smallholder systems and 50-60% in developed markets, creating significant economic inefficiencies and barriers to mechanization. Digital platforms leveraging sharing economy principles have emerged as transformative solutions to improve machinery access, optimize utilization, and reduce per-hectare mechanization costs. This review examines the architecture, mechanisms, and impacts of mobile and web-based platforms facilitating on-demand rental, peer-to-peer sharing, and custom hiring of heavy farm equipment. Key platforms including Hello Tractor, EM3 AgriServices, Tringo, MachineryLink, and regional initiatives integrate geolocation-based matching algorithms, telematics-enabled utilization tracking, integrated payment systems, and insurance mechanisms to connect machinery owners with farmers requiring services. Applications span smallholder access enhancement in Sub-Saharan Africa and South Asia, where platforms have increased mechanization rates by 15-40%, to efficiency optimization in developed markets through dynamic pricing and route optimization. Major challenges include digital literacy gaps, infrastructure constraints, trust-building in peer-to-peer transactions, and regulatory frameworks for liability and insurance. Future developments emphasize artificial intelligence-enhanced demand forecasting, integration with precision agriculture systems, blockchain-based transaction verification, and policy instruments supporting platform scalability. Digital machinery sharing platforms represent a critical pathway toward inclusive, efficient, and sustainable agricultural mechanization globally.