XPostFacto is an open source utility for Mac OS 9 that enables the installation of PowerPC versions of Mac OS X up to Mac OS X v10.4 (Tiger), and Darwin on some PowerPC-based Apple Macintosh systems that are not officially supported by Apple.
The OS X Installer would not run on machines without a G3, G4, G5, or Intel processor by default, but XPostFacto patched the installer to allow it to run.
[3][4] XPostFacto is available for free, but the company offered support for either $10 or $25.
[2] Beige box Power Macs as old as upgraded 7300-era machines are supported.
[6] Engadget gave XPostFacto a negative review for its slowness, stating it "runs like a limp turtle on our old iMac G3.