Mac and iOS: Deliver does what the name suggests -- it delivers messages and files from one Mac or iDevice to another over the local network. It does this with absolutely no configuration and it is super fast. All you have to do is download, install and launch the app on any computer or device on your local network, and you'll be ready to go.
When you launch the app, it'll teach you how to use it but here's the gist. You'll see a little bubble icon. Click or tap it (depending on the platform you're on) and it'll bring up a list of other devices running Deliver. Choose the one you want to send a file or message to and then click/tap the text button (looks like a rectangle with three lines) or the plus button. The text button is for sending a text message and the plus button is for sending a file. Choose what you want and then Deliver will transport it in an instant. I was surprised by how fast a 4MB image made it from my iPhone to my laptop.
On the downside of things, Deliver for Mac is a little buggy. It doesn't always work as expected and it crashed a few times when I tried to drag transfered files away. It also took me a while to get a feel for the interface which was somehow less obvious than the iOS version (despite being similar). The iOS version, on the other hand, worked perfectly so here's hoping the Mac app will catch up in stability soon. Either way, all versions of Deliver. It is a very useful app, so go check it out.