The Nucleo boards all look very similar. The difference is that each board has a different STM32. The ST-Link at the top of the board assist in flexible prototyping. The goal of the Nucleo boards is to provide designers with a quick way to get started with a STM32-based development platform. They can move between the STM32s and they will be able to reuse the header and the extension boards that they are plugging in there. They can either be Arduino shields or they can be using the Morpho extensions.