Power flow controllers (PFCs) can give added benefits in meshed High-Voltage Direct Current (HVDC) grids to increase renewables integration. Interline PFCs have been gaining attention for the last decade due to their easy structure and no need for an external power supply. This paper discusses various interline PFC topologies along with their advantages and disadvantages. The existing topologies are compared with respect to several aspects. These aspects include, for instance, modularity, the number of capacitors, the control range of the PFC, the shape of voltage waveforms inserted by the PFC on the lines, number of devices, the directionality of the current, simplicity of the topology, total power semiconductor rating and losses, and protection of the topologies for external faults. It is concluded that the topology of a PFC for a particular application can be chosen depending on the main goal since the topologies come with their advantages and disadvantages when classified based on various aspects.