Siri is the voice-activated personal assistant for new iPhone 4S. Siri is not a app for iPhone you you can,t download it from App store, Siri is a speech-recognition app. It has both speech input and output, meaning you can speak to it, and it can speak back to you. So that mean it a personal assistant for your iPhone. Now you can enjoy the same app in your Android phone with the Iris. Irsi a new app for android, which works like Siri.
Iris allows you to search on various subjects including conversions, art, literature, history, and biology. You can ask it any question and it will reply you. The app is still not available in android market but developers are working on it and he app will soon be available in android market. You can grab the Iris beta APK from here