"Beginning STM32: Developing with FreeRTOS, libopencm3 and GCC" by Warren Gay is a practical guide focusing on STM32 development using open-source tools, including libopencm3 and GCC. It covers setting up a FOSS toolchain, programming "Blue Pill" and "Black Pill" boards, and implementing multitasking with FreeRTOS. You can find more information about this book on the Apress website.