Abstract-Dynamics of distribution grids are becoming more and more complex to analyze due to their transition from passive networks to active ones. This has necessitated the increase of observability between Transmission and Distribution (T&D) grids for operational security and real-time security assessment. This paper presents an overview of the IDE4L project, funded by the European Commission, where a system of PMU data-based monitoring applications has been developed to facilitate TSO-DSO interactions.Index Terms-DSO, dynamic feeder rating, Kalman filter, mode estimator, PMU, steady state model synthesis, TSO, voltage stability analysis.