If you plan on scanning the tech headlines in the next several months, make sure you don't misread iOS 9 as "OS 9." You will be bitterly disappointed. You will be especially aghast at reports of new features such as multi-user support. In 2015.
For OS's that support PowerPC, we'll have to make due with what we got. Handily, TCH put a list together compiling every OS that ran on PowerPC through the present-day, so pay a visit to OS for PPC and go explore.