From Dave Madison on the Parts Not Included blog:
Lately I’ve been working on a project that will use an Arduino to translate signals from a wireless receiver into USB HID inputs for my computer. I had the perfect microcontroller picked out too: the SparkFun Pro Micro, which uses the Arduino-compatible ATmega32U4 and has enough I/O pins for my project and then some. There’s just one problem – the Pro Micro doesn’t have a USB-A port to plug directly into a computer! Instead it has a micro USB-B port, and requires a short cable to connect it to a PC.
Luckily for me the Pro Micro, like many of SparkFun’s designs, is open source and licensed under Creative Commons Share-alike. So I decided to dive in and modify the design to create my own version of the Pro Micro with a USB-A port!