Bark is the result of a hackathon collaboration between members of several companies.
You choose a dog, then you can bark to everyone within 1 mile of where you are.
There's people barking all over the world already (it was released about an hour ago)
You can find it on the app / play stores here:
And if you’re interested in watching it spread, you can watch all the barks live at http://www.barkstats.com