Many uses Windows and OSX these days. But MorphOS is one of the less known commercially OS’s available for PowerPC compatible computers. MorphOS is a well known operating system within the Amiga community, but outside of it this OS is not so known. However there are some people in this world that uses this OS, which can be seen on the MorphOS users Worldwide map.
Latest MorphOS have reached 3.9. MorphOS got native PowerPC support but it also supports AmigaOS PPC software and AmigaOS 68k software. You can install it for many PowerPC macs with G4 CPU, including PowerMac G5 and SAM460. Next hardware to be supported is AmigaONE X5000 which will be released soon.
Read More about MorphOS here: