SPIDriver by Excamera Labs

SPIDriver is an easy-to-use tool for controlling SPI devices and a great tool to help with quick driver development and debugging. It works with Windows, Mac, and Linux, and has a built-in color screen that shows a live logic-analyzer display of all SPI traffic. It uses a standard FTDI USB serial chip to talk to the PC, so no special drivers need to be installed. The board includes 3.3 and 5 V supplies with voltage and current monitoring. It's kinda like a Bus Pirate with a display and great Python support.