My home automation and monitoring system runs off two separate radio networks; RF12 and XRF. The RF12 network communicates with a JeeNode LED board, which also runs the light strip for the centre cabinet. The XRF network uses a USB stick made by the makers of the XRF radio.
Both of these devices create a serial port instance on the Ubuntu server, and pass through exactly what is sent or received – either PC to radio, or radio to PC. In order for my web apps to communicate with them, I had to find a way to constantly monitor what was received, and also a way to send commands out.