High Quality Content by WIKIPEDIA articles! XPostFacto is an open source utility that enables the installation of PowerPC versions of Mac OS X up to Mac OS 10.5, and Darwin (operating system) on some PowerPC-based Apple Macintosh systems that are not officially supported for them by Apple. XpostFacto - often referred to as "XPF" - runs under Mac OS 9 and allows an unmodified Mac OS X installation disc to be launched on machines which cannot boot Mac OS X unaided. This allows Mac OS X to be installed on certain Mac models which could otherwise only run System 7, Mac OS 8 or Mac OS 9, albeit sometimes with incomplete functionality. For example, it can be used to install Mac OS X v10.2 on a PowerPC 604 equipped Power Macintosh 8600 or 9600.