The Power Systems boxes can run many operating systems, and users can share their opinions here.
IBM i (aka OS/400, i5/OS) is the premier OS on the Power System boxes. Share information with your peers here.
The Linux/open-source operating systems are increasingly popular, and this is the place to share information.
Many Power Systems shops use Microsoft's operating systems, and this is the place to discuss those OSes.
The merge of the System i and the System p put Unix and AIX operating systems run on the Power System boxes.