On sufficiently old/industrial PCs, the parallel port is a pretty usable GPIO header, especially the more modern implementations with bi-directional pins.
It's easy to use one to switch a transistor[1], for instance, and there is a Python library to control the port[2]. An optoisolator is a good idea since computers are expensive and isolation is cheap.
The DonglePi looks nice since it will exposes I2C, SPI, and PWM. I could see it being handy to test out I2C and SPI parts before integrating them into custom boards.
It's easy to use one to switch a transistor[1], for instance, and there is a Python library to control the port[2]. An optoisolator is a good idea since computers are expensive and isolation is cheap.
The DonglePi looks nice since it will exposes I2C, SPI, and PWM. I could see it being handy to test out I2C and SPI parts before integrating them into custom boards.
1. http://www.next.gr/uploads/139-016e0f9471.gif
2. http://pyserial.sourceforge.net/pyparallel.html