FEZ Panda is a tiny open-source board running Microsoft .NET Micro Framework. This means, you can write code with much more efficiency using C# programming language under free Microsoft Visual C# express.
FEZ Panda also includes JTAG access for those who wish to use their own firmware instead of NETMF. Using an Arduino-form-factor, you can use just about any Arduino shield. In addition, many libraries are already included like FAT file system, networking, threading, USB Client, UART, SPI, I2C, GPIO, PWM, ADC, DAC and many more. Includes USB cable.