Um dos sistemas é um Mac? Então olhe para exibição de ar .
Ever wish you had an extra display for your computer? There’s an app for that! With Air Display, you can extend your desktop wirelessly to your iPad, iPhone, iPod touch or Mac as a wireless display.
Se você estiver usando o Linux, então DMX pode ser o que você quer.
Xdmx is proxy X server that provides multi-head support for multiple displays attached to different machines (each of which is running a typical X server). When Xinerama is used with Xdmx, the multiple displays on multiple machines are presented to the user as a single unified screen.
Para o Windows, veja o Maxivista .
MaxiVista allows you to use a Laptop as a second monitor for your primary computer. No extra multi monitor hardware is required. Simply extend program windows across multiple screens as if it were one big monitor.
Veja: link