We present Move Base Flex (MBF), a highly flexible, modular, map-independent, open-source navigation framework for use in ROS. MBF provides modular actions for executing plugins for path planning, motion control, and recovery. These actions define interfaces for external executives to allow highly flexible navigation strategies, which can be intertwined with other robot tasks. MBF has been successfully deployed in a professional setting at customer facilities to control robots in highly dynamic environments. We compare MBF with the well-known move base and present the architecture as well as different deployment approaches, including how MBF can be used with different executives to perform complex navigation tasks interleaved with other robot operations.