In El Capitan, Split view is actually a part of full-screen mode — it just so happens you can have your full-screen app budge over and only take up half of the display, and then choose something else to fill the remaining space. No apps we know of ape this functionality directly, but plenty enable rapid window resizing, meaning you can quickly get windows side-by-side.
Moom ($10) is the best of them, and is very configurable. You can snap windows to edges or corners by dragging them, use a zoom button overlay to draw on a grid to state where you want a window to go, or create custom keyboard shortcuts for throwing windows about.
Even when El Capitan appears, Moom will still be worth having, because it offers so much more than what you’ll get with Apple’s equivalent feature.