Portland-based Avatron, which develops apps which allow your iPad, iPhone, iPod Touch, or Android to act as a second display for your PC, said today that it has launched a new app for Windows. The app allows users to use your second PC as an additional monitor for either your Mac or PC. Avatron said its software, Air Display, allows users to use their second machine as a graphical display, communicating with their main PC over an Ethernet connection or wireless. The firm said the PC and Mac software is free, with the iPad and iPhone version costing $9.99.