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

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.

While I don't believe that there are currently any window managers available for Android devices (except where some manufacturers, like Samsung may build this in) there are some other options that may work for you, depending what you're after, by optionally floating some other apps or features over or alongside your current app.

• There are some third party Android web browsers that can "float" a window over your current window, and can be dismissed or brought to the front very easily: OverSkreen (formerly known as AirBrowser), or Floating Browser Flux

• There are some small utilities like two calculators or Terminals that can also be floated over your current window.

• Quickdesk is an app that can put a floating toolbar over other apps, giving you quick access to other apps.

• If you're finding the keyboard is getting in the way, and you'd rather it floated over other apps, then you may find some of this question's answers helpful: How can I “split” the virtual keyboard when typing on a large display in landscape mode?

• Although it needs custom written widgets/apps, you may also find that the Chameleon Launcher can do what you want as it specialises in arranging tiled windows of information/apps alongside each other (website).