Plenty of Android apps claim to be a Siri-fighter, and new ones appear every other day.
Robin, which just underwent an overhaul, is actually pretty impressive. The new version has a huge button combined with a map view and is really designed for car use, where you can operate most features hands-free (one or two may require a tap on the screen or two).
And Robin talks back, using any voice you have installed. Those of you who have IVONA installed (download all three English voices: US, UK, and Australia) should have much better voice than the built-in Pico TTS.
And Robin will give you a full conversation. You say "tell me a joke", and Robin will answer. It will do context sensitive search based on location. If you search for a location it recognizes, it'll display Yelp link and Nav link. It knows most commands, and if it doesn't, it'll do a Google search for you. It will link to any Nav package you got, either Google Maps or Waze, or even others like Tomtom.
It'll do social updates, voice dial, and the other stuff. It's pretty impressive, and it's free.