In summary, the Nucleo family is a set of very affordable boards that allow engineers to simply try out the STM32 family because they have common headers across all of the boards, both the Arduino connectors and the Morpho headers. There is a large set of expansion boards that are available and those expansion boards could be used with any of the Nucleo boards. This provides a lot of flexibility to evaluate the STM32. Because it comes with the integrated ST-LINK, it is a full environment that can be used to evaluate the development of the STM32 and very importantly it is supported by the free online mbed, which allows designers to evaluate and get started with the Nucleo boards without having to buy an IDE, so it's a low cost and simple way for people to get started with the STM32.