AirDrop is a pretty slick app that was first available in OS X Lion. It basically allows any Mac see any other Mac with the protocol enabled on the network, with no configuration or knowledge of file sharing needed. You just drop a file onto any available AirDrop icon, and your file heads over to that user’s Mac. No muss, no fuss, just simple.
At least, that’s the concept. In reality, I’ve not seen AirDrop ever work that easily. Luckily, there’s an alternative that’s even simpler: Any Send, a free Mac app that lets you send files to any other Mac using WiFi.