PeerTalk is a small iOS and OS X Cocoa library for communicating over USB and TCP.
There are at least three upsides to connecting over USB:
Secure. Only the apps in each end of the USB cable can communicate with each other.
Simple. No entering hostnames, ports and browsing openly announced internet services.
This little thing is something I hacked together for fun and I haven’t spent more than a few days, so there will be bugs. It’s released under an MIT license, thus you can use this for both fun and profit.