If you have e.g. a MacBook of some description (or indeed a Windows machine), and an iPad, you can use the iPad as an additional display. Duet Display works over a USB cable, so is much much smoother and less flakey in operation than old implementations of the general idea using Bluetooth. Works a treat. OK, it won’t magically increase your “productivity” but it assuredly reduces the irritations of window-juggling when working. You can get Duet Display on the app store or from their site. If you don’t know it, a warmly recommended bargain.