multi window - How do I run two programs at once in split-screen?

I have a Nexus 10. I want to split screen to do two things at the same time. Is that possible in Android? 3rd-party apps are acceptable too.

Answer

As of this writing, only a few Android devices offer multi-window functionality out-of-the-box. Samsung built this feature into 4.1.2 OS version for several of their Android tablets (Galaxy Note 10.1 and Galaxy Note 2, for example.)

There are some major drawbacks to this. First, it's a proprietary Samsung feature that only comes with their TouchWiz overlay, and therefore is not compatible with "vanilla" Android OS. Second, apps must be specifically written to support this feature.