Orginal version of AmigaOS required the Motorola 68000 series of 16-bit and 32-bit microprocessors. Then Hyperion Entertainment approched Amiga Inc in 2001 to make a port of AmigaOS to a PowerPC microprocessor.
AmigaOS 4 has had a difficult life, in 2001 Hyperion and Amiga Inc entered an agreement to allow Hyperion to develop a Power PC version of AmigaOS, based on the source code of AmigaOS3.1. Amiga Inc at this time had decided to focus on its Amiga Anywhere platform. It was hoped that a port could be produce in sort order, even Hyperion claimed it could be done in 4 months, however a Developer Pre-Release did not arrive until Oct 2004, 3 years of development. It would take a further 2 years, before a final release in Dec 2006 was OS4 no longer consider a betaOS. This version was only for Eyetech AmigaONE systems. November 2007 finally saw OS4 for classic Amiga PPC equipped systems arrive, OS4 had finally hit the Amiga Market. AmigaOS4.1 arrived in 2008 which continued to improve the OS feature set and added support for ACube Sam systems, later ports where made to A-EON AmigaONE X1000. 2014 saw the release of the so called final edition of AmigaOS4.1 again making minor improving and features for the OS. Since this release very few updates have been released and the only on going work of the OS seemed to be the port of the OS to new hardware, such as AmigaONE X5000 and A1222. During this time also critical parts and third party tools that where part of OS seemed to have changed ownership and management over to A-eon for it Enhanced Software package.
AmigaOS4.2 was announced in 2012 as part of the AmigaONE X1000 development and its main feature was to make AmigaOS finally a milt core supported OS now that it was on hardware with a dual core cpu and the whole computer industry moving in that direction. Development news and progress of this and other future version of the OS has been pretty much silence since 2016 and progress of even the port of AmigaOS4.1 to the A1222 has been plagued with delays.
Its a shame that not just slow development has plagued AmigaOS4 but also legal disputes haven't helped, during its development Amiga Inc and Hyperion sued each other over the rights of AmigaOS4, https://en.wikipedia.org/wiki/History_of_the_AmigaOS_4_dispute This was settled and Hyperion was awarded ownership of AmigaOS4. However 2018 a new lawsuit started between Cloanto and Hyperion over the rights to the ownership of AmigaOS3.1 source code and weather or not Hyperion could make OS3.1.2 this could also indirectly affect AmigaOS4 future developments.
But again it wasn't just Legal problems for AmigaOS4, different companies and developers had different views on the future of the platform and so what was and still is a small market got split, MorphOs and Aros systems arrived at a similar time for the Amiga market and some developers chose to support them platforms over OS4, 2006 to 2008 was consider the Red Vs Blue Wars of which platform was better, this didn't help the overall Amiga community at all with so much trolling and hating a lot users and developers decide to just leave the platform/market altogether.
It feel like the Amiga curse is well and truly present for the AmigaOS4.x with it doggy history. Its a real shame that OS4 never really felt like it had the right resource behind it, but on the whole it is a good stable platform today, and does represent how AmigaOS could still a useful and good OS even in the year 2020.