Download from here. Then make sure you install all the available updates first: Select Tools>Plugins and Check for updates.
If you had a previous installation of Gephi on a Mac, you find find that the launch freezes at “Opening Main Window.” If so, in Finder select Go>Go to folder and navigate to /Users/YourUserName/Library/Application Support, substituting your own user name for YourUserName. Delete the old Gephi folder.