While the Arduino family of boards connect to your computer using a USB virtual serial port, the ATmega ones have an actual serial connection on-board.

Serial Port Monitor from Eltima The Serial Port Monitor software tool from Eltima Software is, in fact, a professional port sniffer and analyzer system utility good for RS232/RS422/RS485 port ...

Eight digital outputs act as the parallel interface. When a byte is received over serial, the individual bits are set on the individual digital lines connected to the printer’s parallel port.

While Octave will never have the rich instrument control options available to MATLAB users, there are still ways to get serial data directly from a connected device into Octave. The Octave: ...

An image from H.D. Moore's presentation on serial server security vulnerabilities, showing an oil and gas infrastructure setup networked with serial port connections. (Click to enlarge.) You ...