Deskreen is a free and open source desktop app that turns any device with a web browser into a secondary screen for your computer over WiFi. It can be used to mirror entire computer display onto any device screen that has a web browser. Also you can select only one application window view to share – very useful for presentation purposes.
The best feature of Deskreen is to use any device as a secondary screen. To have a true extended desktop experience Deskreen should be used with Virtual Display Adapter. Also with no need for Virtual Display Adapter you can have a teleprompter with Deskreen using your tablet or smartphone, for that Deskreen has Flip Screen Mode that mirrors computer screen in web browser of your tablet (aka. flip screen horizontally).
Deskreen comes with support for Windows, Mac and Linux. You can download them for free from Github website here.