When the Nexus 5 launched, it had its own custom launcher, which at that time was called the Google Experience launcher. Google announced the launcher was going to remain exclusive to the device, but as Donald Bell covered there are workarounds to get the Google Experience on other Android devices.
Then earlier this week Google updated the Google Search app and as Droid Life pointed out, it contains some interesting changes. The Google Experience launcher is now named the Google Now launcher and it includes the ability to import your current icon and folder settings.
The Google Now launcher is still only officially available on the Nexus 5, but as with all things Android, there's a workaround. By installing the Google Search update from the Google Play Store, and installing the GoogleHome APK (which comes from the Nexus 5), you can experience the Google Now launcher on nearly any Android device.
By visiting the Droid Life link above you can grab both of the required APKs to make this work. Keep in mind you'll only need to download the Google Search update if it hasn't shown up for you in the Play Store yet.
After installing both APKs you should be prompted to select your preferred launcher the next time you tap on your home button.