The multi-monitor display extension app, spacedesk lets you use other devices and computers on your LAN (Local Area Network) as monitors for your Windows desktop. At least 2 machines are needed to operate spacedesk.

Deskreen turns any device with a web browser to a second screen for your computer

Tab Display seamlessly transforms your tablet into a second monitor, allowing you to extend your screen and stream the virtual display directly to your device. This app supports both Android tablets and iPads for use with Windows and Mac environments.

Duet Display is a remote desktop application that transforms an iPad into a second display for a Mac computer. It allows Mac apps to be transferred to the iPad, providing additional screen space for multi-tasking.

Turn your iPad into a wireless second display.

Turn your iPad, Android tablet, Kindle or smartphone into a high performance extra monitor for your computer

Yam Display turns your iPad/iPhone into an external monitor for your Mac. Wired by USB, browse documents or watch videos without delay. Touch your Mac and pinch to zoom on beautiful retina display. For multitasking enabled iPads, you can utilize every single pixel of your screen...

Smart devices become monitors by connecting them to a PC via USB! The Convenient Connect TwomonUSB

Use your iPad as a wireless display, to extend your Mac desktop. Ever wish you had an extra display for your computer? There’s an app for that! With Air Display, you can use your iPad as an additional monitor for your Mac (Windows no longer supported)

Turn your iPad/iPhone or Android tablet or smartphone into a convenient side monitor for your Windows or Mac desktop. iDisplay is a universal app specially optimized for iPad, iPhone, iPod Touch, and Android devices screens.