If you are jailbroken then you are lucky! You can
get MultiTasking like in iPad on older iPhones, iPads & iPod Touch. If you
aren’t jailbroken yet, Here’s how to jailbreak iOS 9? 
Follow these steps to get this tweak

Step 1: Go to cydia–Sources & add this
source: Hackyouriphone Repo

Step
2
:
Search for ‘MEDUSA’ & install it.
Step 3: Also install “ROTATEPLUS”. You need
to add source to install this tweak. Source: Xarold Repo (You
need this tweak to use Medusa in landscape mode)
Step 4: Go to Settings—Scroll Down to
Rotate+ & Enable everything.
To use this just swipe left from the edge and use
another app at the same time.
Enjoy ! You are done.