Apps with 'Second monitor support' feature

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

A small, fun app that helps you use your iPad as an external HDMI display for any camera, video game console, or even VHS.

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

CamX - USB Camera is a multifunctional iOS app that converts your device into a portable video capture tool, capable of recording from various sources, and can also serve as a gaming console display or secondary screen.

Turn your iPad into a professional drawing tablet.

Turn your iPad into a wireless second display.

Genki Studio is a software that turns your iPad into a portable monitor and video capture device. It connects to a Genki ShadowCast or any USB UVC device, with features like external monitor support, Apple Pencil markup, and multitasking.

GiMeSpace KVMShare Pro is one of the very few real KVM software sollutions that not only shares mouse and keyboard but really allows you to share video in the form of windows on the screen of connected computers while using minimal bandwidth.

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.

Make your iPad/tablet/computer into a secondary monitor on Linux. - GitHub - kbumsik/VirtScreen: Make your iPad/tablet/computer into a secondary monitor on Linux.

AirMyPC allows you to wirelessly AirPlay mirror your Windows PC screen and sound to your TV through 2nd/3rd AppleTV.