What's so great about it? Each post will be shared automatically to 4 other users near your area. If those users do like your post, they can share it to 4 others also...
The basic idea of Plague is creating viral post. The interface is simple and nice. You can see stats about your own posts, where they were seen and how far they have spread. From what I could understand, each post can survive 7 days.
You can get it on the Apple Store:
Or on the Google Play Store:
Be viral, get Plague!