I’ve had the good fortune to be accepted as an occasional contributor to the Hack a Day blog. (Hack being slang for an informal method of engineering, not criminal acts!)
My first substantive tutorial for the site describes the use of FTDI Bitbang Mode, a method of using a common, inexpensive USB-to-serial adapter as a quick & dirty GPIO interface. This facilitates the sort of prototyping typically done using microcontrollers, but in the comfortable and unconstrained development environment of mainstream PCs. The technique is particularly well-suited to SPI-type protocols; I’ve had this communicating with shift registers, LED driver chips and even video overlay ICs, as well as reading various optical rotary and linear encoders.