One very popular and fun iPhone / iPad app that I love to use is Avatron Software's Air Display. As we described in a First Look back in May of 2010, Air Display turns an iOS device into a small wireless monitor that can be used to display app windows from a Mac or Windows computer.
Now Avatron has made Air Display even more useful by creating a Mac app to do the same thing. Air Display for Mac (US$19.99 in the Mac App Store) is a bit more expensive than its iOS sibling, but it's also more capable than the mobile device version -- especially if you have a second Mac with a large screen.
Similar to Air Display for iOS, Air Display turns a Mac into a wireless display for extending the desktop of your other Mac or Windows computer. Air Display is available in the Mac App Store, and needs to be installed on the Mac that you want to turn into a secondary display. You then need to visit the Avatron website to download the host software for your primary computer. As noted, that computer can be either a Mac (running Snow Leopard) or a Windows PC (running XP, Vista or 7). You do have to reboot the host computer during the installation process. The same host software works with both iOS and Mac extended displays.
You can connect the two computers via Ethernet for ultra-fast response, or use Wi-Fi for that true "Air Display" experience. The two devices just need to be on the same network in order to work. And how does it work? Well, I started writing this review a few weeks ago when the app first appeared, and I couldn't get it to work at all. I turned off my firewall, tried some tricks with opening ports on my AirPort Extreme and did some other things to try to get it to work, all to no avail. This morning there was an update available for my host 27" iMac that appears to have fixed some networking issue, because Air Display for Mac is working beautifully for me now.
Air Display is perfect for those situations where you need to have some additional screen real estate, have another Mac, but don't have another monitor. In my situation, I'm thinking of using this for some of the many windows that I have open when I do TUAW TV Live every week. I need to monitor them, but not necessarily type into them, so I'll just have them open and viewable on my MacBook Air.
Over an 802.11g Wi-Fi connection, I found there to be a slight amount of lag. When moving a window on the MacBook Air that was hosted from the iMac, the window refresh was a bit jerky. That could be resolved via an Ethernet connection, although I didn't try that. Frankly, the refresh rate isn't an issue, because if I put a window on my MacBook Air, it's going to stay there -- I'm not going to be moving it around a lot.
If there's one wish I had for Air Display, it's that it would pump out video to two devices (Mac and iPad, for example) at once. You can switch between your extended displays, but it would be very nice to have a window or two open on the MacBook Air and another on the iPad. Knowing the folks at Avatron, they'll probably figure out a way to do it.
Anyone who needs just a bit more display space should seriously look into Air Display for Mac or the iOS versions. Air Display is well-suited for providing that extra pixel real estate, and if you already have the other screen in the form of another Mac or iOS device, at much less cost than buying another monitor.