Android: With the advent of Android 4.1, handsets with virtual buttons (like the Nexus line and the Moto X) have a gesture built-in to quickly get to Google Now. If you're satisfied with the millions of other ways to get to Google Now, Home Button Launcher can redirect that gesture to something more useful.
The app allows you to add one or multiple shortcuts to the swipe-up gesture on devices with software navigation buttons. You can either elect to have the app ask you every time, giving you a choice, or set it to immediately open the app if you've only chosen one shortcut. While they're not perfectly supported, the developer states this app may also work when doing a long-press on a physical home button with devices like the newer HTC One line.