As renewable and converter-interfaced energy generation becomes increasingly prominent, power systems are more susceptible to frequency and voltage oscillations under sudden power perturbations. Simultaneously, dc-based power systems are gaining popularity due to their advantages over traditional ac systems in specific applications. These trends highlight the growing need for advanced time-domain simulation tools to study the frequency stability, in order to accurately represent the dynamic behavior of converter-dominated, hybrid ac/dc power systems, such as the rate of change of frequency (RoCoF) in ac systems, and rate of change of voltage (RoCoV) in dc ones. This chapter introduces a Dynamic Frequency Power Flow (DFPF) tool designed to address these challenges, while it is compared to other dynamic simulation approaches for power systems. The DFPF tool integrates classical static power flow algorithms with simplified models of generators and grid-connected devices, implemented within the Simulink® environment. This framework enables the study of oscillations associated with the electromechanical phenomena of rotating generators and the critical control dynamics of grid-connected converters. Besides, aspects like the renewable generation and the emulation of inertia can be assessed in ac, dc, and hybrid power systems. One of the key advantages of the proposed tool is its low computational burden, which ensures efficient simulations and enables to simulate time spans in the order of hours to efficiently study the effect of control or physical parameter variations in the performance of the system. Furthermore, the Simulink® interface simplifies the creation of new test scenarios when developing DFPF simulations, allowing users to carry out dynamic power system studies with remarkable ease and efficiency.