That feature is Apple's Metal API, which was originally designed for iOS 8, and which allows developers more direct access to GPU hardware. In theory, the new API will enable developers to optimize their GPU-intensive apps for notable boosts in rendering performance.

Adobe has already announced that it will be adopting the Metal framework for all of its Creative Cloud apps for OSX. It also announced that in its testing of After Effects, they saw impressive performance gains of roughly 8x when rendering. It's hard to say what exactly this will mean for the other video and photo apps in Adobe's CC suite, but any boosts in graphics performance are always welcome in my book.

If you're wondering what else is coming to OSX El Capitan, here's a quick summary video of the new features from TechnoBuffalo:

Apple also announced that it is working with other software companies such as The Foundry and AutoDesk to implement the Metal API. Like previous iterations of OSX, El Capitan will be a free upgrade and will likely be released to the public in Fall of 2015.