AirPlay Mirroring requires a second-generation Apple TV or later, and is supported on the following Mac models: iMac (Mid 2011 or newer), Mac mini (Mid 2011 or newer), MacBook Air (Mid 2011 or newer), and MacBook Pro (Early 2011 or newer).
Several Apple Articles Regarding AirPlay
He was asking if there is any 3rd party apps that would allow, iPads or any other AirPlay enabled iOS device to AirPlay to the iMac (Like you can to a TV) not wether he can stream his iMac display to a TV. I am wondering the same thing... what are anygood preferably free apps out there that are good, and allow that capability.
This application for your mac will allow you to airplay from your iOS device to your iMac. It's $15 bucks. There may be something cheaper or free out there, but this is the one I know of off-hand.