iPhone cases aren't normally too exciting, because most of them simply protect your phone while trying to not look too ugly. But not every case is boring, especially those that actually add some functionality to your iPhone, which is exactly what the Lunecase does.
Every electronic device radiates a tiny amount of electronic power through its case, and the Lunecase uses this minuscule electric charge to light up two indicators built into the back of the case. One lets you know when there's an incoming voice call, while the other alerts you to arriving SMS text messages. That could be really useful if you have the ringer and text alerts turned off in a quiet restaurant or library, and you don't want to stare at the screen to see what's happening in the outside world. To differentiate between texts and voice calls the Lunecase determines which frequency the transmission is using, and that's pretty clever by itself.
The beauty of the Lunecase is that it can do its work without any batteries, charging, or physical connection to the iPhone. Simply snap it on and it works right out of the box. Because it uses power that would be lost by the iPhone anyway, the Lunecase won't hurt your phone's battery life. My only concern is whether the case affects signal strength in any way. I once had an iPhone case that would cut your signal by a couple of bars, so it can be an issue.
The Lunecase was developed by a team called Concepter in Ukraine, and is being funded as a Kickstarter project. Currently, all of the lowest cost donations that will get you a Lunecase are sold out, but as of this post you can still get in for $39, which is $11 off the retail price. Deliveries are scheduled to start in August.