since you only really need three lines to do serial communication (and in this case we are not using hardware flow control, which would require two extra lines), a DE-9 to stereo jack is all you need for serial communication with anything with an embedded microprocessor.
The two cases I've used this are a serial programming cable to a TI cable modem, so you could get boot messages and command line access for firmware upgrade purposes; and a OneTouch UltraMini Glucose meter. Here the parent company will sell you an overpriced cable just so you can download your timestamped historic testing data into their "free" software app.