Airfoil allows its user to send any audio to one or more AirPort Express units in sync and to other local Macs! As Rogue Amoeba puts it: "It's your audio - everywhere." Need any more clues? If you've already used Airfoil 3 (updated just over a month ago), you're good to go with this free trial of Airfoil 3.1.0, which adds Apple TV support.

So, here's what it does. You can use Airfoil to take audio from any application whatsoever and send it to your AirPort Express units, Apple TVs and Macs and PCs running Airfoil Speakers! Any Mac or Windows machine can be turned into a virtual AirPort Express with Airfoil Speakers - you can send audio from Airfoil to that machine, just like an AirPort Express!

Of course, there are other sources from which you can drain audio and stream it to the AirPort Express, Mac or Apple TV, such as RealPlayer, Windows Media Player, QuickTime Player, web-based applications like Pandora, Last.fm, or audio devices like RadioSHARK, XM and Sirius radios, if you've got anything of the sort laying around the house.

For example, here's how to use it with your Apple TV: "With the latest Apple TV software and Airfoil, you can send audio to your Apple TV too! Open Airfoil and your Apple TV will show up in the list of available outputs, ready and waiting for your audio. Just click the Transmit button and Airfoil will send audio to the Apple TV!," says rogueamoeba.com.

But there's even more. This one you'll find particularly interesting: with Airfoil Video Player, you can watch video on your Mac and send the audio to your AirPort Express, having it all play in perfect sync.

Airfoil Video Player supports all QuickTime Player native formats, formats by the Perian plug-in, and by any additional plug-ins you might have installed, including Flip4Mac for WMV support. Airfoil Video Player also features preliminary support for DVD playback, according to Rogue Ameoba.