AmigaOS 4.1 Final Edition (Classic PPC) for Amiga 1200 with BlizzardPPC or Amiga 3000/4000 with CyberstormPPC accelerator.
AmigaOS 4.1 was released in September of 2008 and has seen no less than 6 free major updates and at least 88 smaller updates released through AmiUpdate. New functionality in AmigaOS 4.1 Final Edition includes but is not limited to:

 Extended memory functionality (beneficial for all supported platforms even those platforms which cannot be equipped with more than 2GB)

 Most powerful console for AmigaOS

 New Intuition features

 New Workbench features

 Much improved DOS

 New unified graphics library with RTG support which allows for (current and future) very substantial general and platform specific performance optimizations e.g. through the use of on-chip DMA engines (present on recently released hardware going back to the Sam440)

 Updated Python port

 Installation graphics, new icons and back-drops by Martin Merz

 Countless minor updates, increased functionality and bug-fixes.
AmigaOS 4.1 Final Edition requires NO previous version of AmigaOS 4.x and is a standalone product, quite possibly the most affordable version of AmigaOS ever to be released.
This now allows current users of AmigaOS 4.1 to install a complete original version of AmigaOS 4.1 without subsequently needing to download or apply 6 updates and countless minor updates.
Users are nevertheless recommended to register their copy of AmigaOS 4.1 Final Edition on the Hyperion Entertainment website as this will be required for downloading possible future updates and bug fixes.
System Requirements:

 Amiga 1200 with Blizzard PPC and 128mb or more

 Amiga 3000/4000 with Cyberstorm PPC and 128mb or more

 Graphics card recommended