AppSales is a website which collects all the discount sales on the play store. You can either visit the website or can install their application. They have posted about a special deal which offers GO Launcher Prime for free. What you will have to do is, Install Go launcher (Not Prime) and go to Preferences > About GO Launcher EX > Enter Activation code shown on the image below.
The Prime offers
More than 6 transition effects
Switch between running tasks using side dock
Gestures to access app faster
This offer ends on June 1st. Grab it fast.