Utter! is different from other options, because of its ability for customization, and because of its huge number of commands that link deeply into the Android system. This isn't just an app that will answer questions, post to social networks, open apps, and call people (although it can do all those things). Utter can also toggle WiFi or Bluetooth,
Possibly the best part of Utter! is that you can also create custom voice commands, and you can initiate commands in a variety of ways. There is obviously an icon trigger, but you can also wake the app by shaking your device, or waving in front of your device (though this didn't work on our Galaxy Nexus).
Utter can interact with a number of apps like Facebook, Twitter, Evernote, IMDb, and Tasker, with planned integration for Google+ and others. There are root commands to boot into recovery, and more.
Of course, this is still a beta app, so a lot of things don't work, and some of the commands require a very specific phrase, which can be annoying, but it is definitely a great start, and we can't wait to see what comes next.
Utter! beta is available for any Android device running 2.3 or higher, and is free in the Google Play Store.