iOS/Mac: We've seen plenty of options for display mirroring between a Mac and an iPad, but they tend to be laggy because they work over Wi-Fi. Duet Display fixes that problem by only working over a wired connection.
Duet Display turns your iPad into a second monitor and works about as you'd expect. Using a free Mac app, you can push your screen over to the iPad. You can send a high quality retina signal or a regular one. You can also choose between 60 and 30 fps. Duet Display is simple, but it's fast, easy to use and works great. That said, MacWorld notes that if you're on a Retina MacBook, you might notice some extra-high CPU usage, so pay attention to that if you're pushing the retina signal over.