This app was mentioned in 7 comments, with an average of 1.86 upvotes
Android actually has true multitasking, something Apple's iOS lacks. Android apps can actually run in the background as they please, if you have them open, whereas iOS kills those resources. Now, Google didn't build in full feature support for multiwindow into stock Android, but they left it easy(ish) for developers to implement. (Or, these very same features can make stuff like this possible.) As others have mentioned, Samsung's had multiwindow as an official feature for a long time, and they're not the only manufacturer to do this. In almost all cases, you should be able to mod in multiwindow support on an Android device with community-built tools / apps. Now, though, Google's realized a lot of people want this, and are, if the development information is to be believed, finally implementing this into stock Android with the next big release.
Another interesting point: Many other mobile OSes, including Windows for Tablets and Ubuntu Touch, already have splitscreen / multiwindow available.
Are you referring to the small apps?
If so, maybe you could try this.
I found Tiny Apps. It's basically Sony's Small Apps, but for any Android skin.
Try out this app: https://play.google.com/store/apps/details?id=com.ragingtools.airapps
linkme: tiny apps
only works for /r/Android then
https://play.google.com/store/apps/details?id=com.ragingtools.airapps
Check out Tiny Apps
https://play.google.com/store/apps/details?id=com.ragingtools.airapps