Duet Display turns iPad into a “Cintiq” for Mac or Windows
Like the Astropad app, Duet Display is an app, created by former Apple engineers, that turns your iPad or iPhone into an input device or second monitor, and it’s now made for both Mac and PC. It works without lag because uses a USB connection rather than Wi-fi. (you can use your Lightning Connector to USB).
First, you download it to your Mac or Windows PC from the Duet Display site, then go to the iTunes store to download the app for iPad. It works with all iPads running iOS7 and up, and all Mac and Windows computers (laptops and desktops) running OS X 10.9 or Windows 7 and later (though I have written them to get clarification on whether it’s OK for Windows 10 as their site says 8.1, so I will update this post after I hear back). Apparently, using a Retina MacBook with it can spike CPU usage.
You can still use graphics tablets and Cintiqs attached to the computer at the same time.
With the Duet, the iPad still won’t give you pressure sensitivity or palm rejection unless you use certain drawing styluses and apps; these use Bluetooth.
More info at duetdisplay.com.