GiHub for Mac is a pretty powerful tool that has always aimed to make code sharing easier for all and now, it has taken that to the next level with the release of a an even simpler, faster GitHub for Mac. The update is noted as a significant one that brings a simplified navigation and a renewed focus on your cloned repositories.
Simplified Navigation - The sidebar now features all your repositories grouped by their origin, and the new toolbar lets you create, clone, and publish additional repositories quickly. You can also press ⇧⌘O to filter local repositories from those associated with GitHub or GitHub Enterprise, and switch between them.
Cloning repositories from GitHub - Fewer steps are required to clone repositories from GitHub Enterprise or GitHub.com. You can now press ⌃⌘O, type the repository name, and then press Enter to clone the repositories you want and need.
Switching and creating new branches - The branch popover (⌘B) has moved to the new toolbar, and now has a "Recent Branches" section that provides a convenient way to switch between all of your in-progress branches. Branch creation (⇧⌘N) has moved to its own popover, and you can now create a new branch from any existing branch.
The release comes shortly after the Windows v2.0 version and helps bring the two apps closer together in terms of how they work. Taking a quick run through, it's pretty awesome. If you're a big user of GitHub you need this in your life.
You can update through the GitHub for Mac app itself by opening the "GitHub" menu, then "Check For Updates or you can download the new release from the GitHub for Mac site itself.
Also of note, this release and future releases of GitHub for Mac require OS X 10.8 or later so if you're running OS X 10.7 or lower, you'll need to update in order to use GitHub for Mac.
Source: GitHub Blog