Graph is a native Windows application but can be run on a Mac through Wine. The link below allows you to download a package with both Graph and Wine. When downloaded OS X will extract the file Graph.app in your Download folder. You can just move it to the Applications folder and afterwards start Graph from the Launchpad.
The package will run Graph on a Mac with Wine as a compatibility layer. This means that some minor problems and incompatibilities are to be expected. In addition this is a beta version, which means that Graph may contain some bugs and unfinished features as well.
In the future a native OS X version of Graph may be available.