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.<p>This is how I also learned that dirt-cheap PC motherboards <i>still</i> have parallel ports built in.  The higher-end ones generally don't.