The STM32 Nucleo boards allow anyone to try out new ideas and to quickly create prototypes with any STM32 MCU.
STM32 Nucleo boards can easily be extended with a large number of specialized application hardware add ons (Arduino Uno Rev3 and ST morpho connectors on Nucleo-144 and Nucleo-64, ST Zio connectors on Nucleo-144, Arduino Nano connectors on Nucleo-32). The STM32 Nucleo boards integrate an ST-Link debugger/programmer, so there is no need for a separate probe.
All STM32 Nucleo users have free access to the mbed online resources (compiler, C/C++ SDK, and developer community) at www.mbed.org.
At the moment I am using the NUcleo-F334R8, here are some of the features
STM32 microcontroller with LQFP64 package
Two types of extension resources
Arduino Uno Revision 3 connectivity
STMicroelectronics Morpho extension pin headers for full access to all STM32 I/Os
On-board ST-LINK/V2-1 debugger/programmer with SWD connector
selection-mode switch to use the kit as a standalone ST-LINK/V2-1
Flexible board power supply
USB VBUS or external source(3.3 V, 5 V, 7 – 12 V)
Power management access point
USB communication (LD1), user LED (LD2), power LED (LD3)
Two push buttons: USER and RESET
USB re-enumeration capability: three different interfaces supported on USB
Virtual Com port
Supported by wide choice of Integrated Development Environments (IDEs) including IAR™, Keil®, GCC-based IDEs
Here is the pinout