The void left by the parallel port
I found out about the CNC thing recently while trying to get a hobbyist CNC machine set up.  My immediate reaction was "Parallel ports?  What is this, 1985?"  Turns out, there isn't really any getting around it.  It's parallel port or GTFO.This is how I also learned that dirt-cheap PC motherboards still have parallel ports built in.  The higher-end ones generally don't.