AirParrot uses AirPlay to mirror your Mac's screen to Apple TV, wirelessly. This is great for Macs that are older than mid-2011 as OS X 10.8's AirPlay mirroring does not work on them.
What's New Version 1.5.5: Resolves an issue when attempting to connect audio to Apple TV OS 7.0
Requirements: OS X 10.6 or later
http://www.airsquirrels.com/airparrot/
