Google announced on Google+ they are bringing the Nexus 5 feature of Google Now embedded throughout the device to other Android devices through the Google Now Launcher.
Google Now Launcher enables Google Now features natively throughout your Android device. Tap home and then swipe right to access Google Now cards or when you see the search box at the top of your screen, you can say “Ok Google” (if you’re in the US, UK, or Canada).
Here is an large animated GIF (sorry if it takes a while to download):
If you have a Nexus or Google Play edition device with Android 4.4 KitKat you can download the Google Now Launcher over here.
Forum discussion at Google+.