The single display gives you your local time, the position of the sun, the rise and set times of the sun and moon (and the 5 brightest planets), twilight start and end times, the current moon phase, a display of day and night on a world map, the current day and date (with a leap year indicator), and the ability to move forward or backward in time in order to see different planetary alignments and sun positions.
The app is certainly nice for star gazers, and it's also handy for photographers who may be looking for the best time of day to shoot outdoors.
The app runs in either portrait or landscape mode, and it looks great either way. In some ways, the app reminds me of the wonderful Spilhaus Space Clock that was sold in the 60's by Edmund Scientific. It didn't display as much as this clock does, but it was pretty on a desk or a mantle, and it was something that everyone wanted to look at and interact with.
So, here's a modern day space clock, combined with an orrery, and it costs less than a dollar. I find the information presented by Emerald Observatory to be very useful, and it is beautiful to watch as it changes during the day. I'd love to see an iPhone version of this app as well. The developers have done a beautiful iPhone app called Emerald Chronometer that emulates several very complex watches on screen, and some of them include the features in Emerald Observatory.