When Matt Podwysocki (@MattPodwysocki) added a todo item on one Android device and we watched the data synchronize and then quickly update on another, I have to say I wasn't so impressed. But when he told me than neither device had an internet connection, my interest was piqued.
Thali (thaliproject.org) is an experimental framework that allows mobile devices to discover and connect directly to one another. It's based on direct wifi, which has been around for a long time, but utilizing it inevitably involves a lot of ceremony. Thali does away with the ceremony.
Matt explains it all very well in this episode of CodeChat. Enjoy.