When OpenOffice was first released it was available for Linux distros and Windows natively, but it ran on Mac under Unix. A company called NeoOffice responded by forking the code into their own distribution for the Mac.
For the past 5 or 6 years LibreOffice and OpenOffice have run natively on Mac, but NeoOffice is still being developed. The suite is being sold through the Mac App Store for $29.99.
It has some different features than it's other open-source counterparts. These include being able to sync with iCloud and having independent floating windows that are common to a lot of Mac applications.
This article will compare the two office suites.