As the title clearly indicates, Google Now Launcher is the official launcher provided by this well-known company, that can be used on devices running Android 4.1 (Jelly Bean) or higher. If your current smartphone is a part of the Nexus 5 series, you already have this solution installed by default and you don't have to download it. Its design is quite lightweight and simple, displaying on the home screen the Google search bar and your favorite applications.
By swiping right from your Home screen, you can access the Google Now cards, a section which displays a plethora of information regarding sports events, instant messaging notifications, and other interesting data. In case you want to search by using your voice or to send various commands, the app requires you to start by saying "Ok Google". All of your installed apps and video games are being shown inside a separate window where you can scroll up and down to see them all.
If you're looking for some specific application, you should use the search box located at the top of the screen. Just as other launchers out there, this one allows you to change the wallpaper used for the background and to add various widgets on your screen.