At last, after various leaks and lots of rumours flying around everywhere, Google Now is available on iOS. Obviously the main difference between the iOS and Android version is that the Android version is a lot more integrated, allowing you to access it from anywhere on the OS.
The iOS version does support cards and it has some nice integration with other Google apps. One example would be navigating. I tried to navigate to a destination, it'll show up but then requires an extra tap to open it up in Google Maps, but from there it'll put you directly into navigation.
It's nice to have it on iOS but if you've used the Android version you'll know how much better it is.
Google Now is integrated into the Google Search app, so it's not a standalone app.