Replace the Google Now shortcut with any app you like with Slide. If you don't have a soft home button with a shortcut to Google Now, This app is probably not going to be useful to you.
Under development. This is far from complete. I've only tested on my Nexus 4.
Source can be found here: https://github.com/ggmathur/android-slide
* Leaves "ghost" app behind
* No visual acknowledgement that an app was selected
* Application list is slow to load
* Noticeable "jump" when launching shortcut.
* Doesn't seem to work on the Nexus 7 if you have multiple accounts.
Things I want to add:
* A better icon
* Select from a list of apps
* Trigger an action
* Explore other forms of shortcuts/gestuers