Prominent features compared to other operating systems or previous versions of AmigaOS:
Instant off / fast reboot: An oft-touted feature is that AmigaOS can be switched off in an instant by just hitting the off switch (if the filesystem is not writing to a disk, which could corrupt entire system).
Workbench screen in front, web browser screen behind.
Screens: You can have as many different screens as you like for any purpose, each with its own application on it; or you can open a public screen which several applications can share. Switching between different screens takes an instant, and you can come back to an application and find it exactly how you left it. It is even possible to drag the current screen down to reveal another screen behind it, (even if they have different display resolutions) so that you can view two screens simultaneously, or even drag and drop files and other content from one screen to another.
Menuing: The menu bar appears at the top of the screen when the right mouse button is pressed down and disappears when it is not needed, thus reducing screen clutter and giving more room to work.
Descriptive file structure: Operating system files are divided up into clearly labelled drawers (folders). For example, all libraries are stored in „Libs:“ standard virtual device and absolute path finder for „Libs“ directory, Fonts are all in „Fonts:“ absolute locator, the files for language localization are all stored in „Locale:“ and so on.
RAM disk: A virtual hard drive, it acts like any other disk, and stores files and data in memory rather than on your actual hard drive. The RAM disk is dynamically resizable and takes up only as much of your memory as it needs to. It can be used as a temporary store for your own purposes or as a place for software installers to put temporary files, and is cleared out at reboot so you won’t be cluttering up your computer with thousands of unnecessary files that bog down your system. Additionally there is an optional RAD disk, a recoverable version of the RAM disk, which preserves contents after a reboot.
Datatypes: Recognises and handles file types: displaying a picture, playing a music file, decoding a video file, rendering a web page etc. Any application can access Datatypes transparently, and thus have the ability to use any file that you have a Datatype for.
Icon handling: A file can have a default icon representing the type of file or a custom icon specific to the individual file. Additionally icons can store extra commands and metadata about the associated file — which program to open it in, for example.
Assigning devices: Instead of assigning drives (devices) a letter or fixed label, each drive can be given a name. Drives can be given more than one name so the system always knows where things are, if it is the system boot drive it is also known as „Sys:“. Areas of hard drive can be assigned a label as if they were a virtual disk. For example, it is possible to mount MP3 players as „MP3:“ and external networked resources as logical devices.
Booted from AmigaOS 4.1 Update 1 Live CD.
Live CD: The OS4 installation CD can be used as a Live CD.
Dockies: It is a fully configurable docking bar for icons, allowing quick access to most used applications. These dock bar icons, „Dockies“, are fully dynamic, which means they can show real-time content and act as useful micro tools. A Docky might act as a magnifying glass, display the time, or show you the latest weather forecast or stock market information direct from the Internet.
Scripting: Implemented scripting as a fundamental feature. Using the AREXX scripting language and Python it is possible to automate, integrate and remote control almost every application and function of the computer. Function sets and tools from several applications can be brought together into a single, integrated interface to allow the most complex jobs to be performed with the utmost simplicity.
A visit from the Grim Reaper.
The Grim Reaper: The „Guru Meditation“ is replaced by „The Grim Reaper“, a crash handling system that attempts to catch crashes and attempts to stop them from getting out of control. It can provide complete information about the crash and optionally kill the offending task and free some of the resources it was using.
AmiUpdate: Is an updating system designed purely for the latest incarnation of the AmigaOS 4. It is able to update OS files and also all Amiga programs which are registered to use the same update program that is standard for Amiga. Updating AmigaOS requires only few libraries to be put in standard OS location „Libs:“, „Fonts:“ etc. This leaves Amiga users with a minimal knowledge of the system almost free to perform by hand the update of the system files.
USB 2.0 (EHCI) support; Updated MUI (for easier porting of MUI 4 applications)
22 December 2011
Emulation drawer with AmigaOS 3.x ROMs and Workbench files; RunInUAE contribution
28 January 2012, 16 August 2012
First public release for AmigaOne X1000, later for other platforms. Improved Warp3D and IDE drivers; optimized DMA copy support for Sam440ep and Sam460ex systems; improved Classic compatibility (support for Catweasel)
After Commodore filed for bankruptcy in 1994, its name and IP rights, including Amiga, were sold to Escom. Escom kept the Amiga products and sold the Commodore name on to Tulip. Escom went bankrupt in 1997 and sold the Amiga IP to Gateway 2000 (now only Gateway). On 27 December 1999, Gateway sold the Amiga name and rights to Amino Development, who changed the company name to Amiga Inc once the assets had been acquired. The ‘Amino’ Amiga Inc and the ‘KMOS’ Amiga Inc are seen by Hyperion as legally distinct entities, contracts to one are of no relevance to the other.
Hyperion’s OS4 project
Hyperion Entertainment has released AmigaOS 4 (OS4) to the public in 2004. The five year development process led to accusations of vapourware and producing a modernPowerPC OS, given that Hyperion claimed that they had the original AmigaOS 3.1 source codes to reference (a claim later proven accurate). This was made worse by the apparent much more rapid progress and maturity of competitor and alternative AmigaOS clone MorphOS, which had been begun several years earlier. Perhaps the most important feature of OS4 as regards the legal dispute is the presence of an entirely new PowerPC native kernel. ExecSG replaces the original Amiga Exec is claimed entirely the work and property of Hyperion’s subcontracted developers Thomas and Hans-Joerg Frieden. Neither Amiga Inc nor Hyperion actually own ExecSG, so technically cannot demand or hand it over, leaving the OS with fragmented and confused ownership.
The supposed rebirth of Amiga
AmigaOne X1000 running AmigaOS 4.1
In 2007 The Inquirer reported  that the Amiga was inching closer to rebirth with the long-awaited release of AmigaOS 4.0, a new PowerPC-native version of the classic AmigaOS (Motorola 68k) from the 1980s. This new PowerPC OS would run on theAmigaOne machines, now out of production, which could only run Linux while waiting for the new PowerPC OS to be released. The year after, Amiga Inc also announced a new AmigaOS 4 compatible system that would be available shortly. The new machine was neither Genesi’s Efika, nor the project codenamed Samantha, (now known as the Sam440ep from ACube Systems). The new hardware was from a new entrant, the Canadian company ACK Software Controls, and would have consisted of a budget and advanced model.
Four days after Amiga Inc announced the new Amiga OS4 (OS4) compatible machines they sued Hyperion Entertainment(Hyperion). Amiga Inc stated that it decided to produce a PowerPC version of AmigaOS in 2001 and on November 3, 2001 they signed a contract with Hyperion, (then a game developer for the 68k Amiga platform as well as Linux and Macintosh). Amiga Inc. gave Hyperion access to the sources of the last Commodore version, AmigaOS 3.1, but access to the post-Commodore versions OS3.5 and 3.9 had to be purchased from the third party responsible for their development since Haage & Parnter (developers of OS 3.5 and 3.9) never returned their AmigaOS source code to Amiga Inc.
Amiga Inc also said that its contract allowed Hyperion to use Amiga trademarks in the promotion of OS4 on Eyetech’s AmigaOne and stipulated that Hyperion should make its best efforts to deliver OS4 by March 1, 2002. A port of an elderly Operating System (68k) for an entirely different processor architecture (PowerPC) in just four months, an optimistic target that Hyperion failed to meet.
According to Amiga Inc, the contract permits the purchase of the full sources of OS4 from Hyperion for US$25,000. The court filing says that Amiga Inc paid this sometime in April–May 2003, to keep Hyperion from going bankrupt, and that between then and November 21, 2006 Amiga Inc paid another $7,200, then $8,850 more which it says Hyperion said was owing.
Furthermore, in the filing, Amiga Inc. President Bill McEwen revealed that Amiga Inc still hasn’t received the sources for OS4, that he’s discovered that much of its development was outsourced to third party contract developers and that it’s not clear if Hyperion has all the rights to this external work. Eventually, after five years and $41,050, on 21 November 2006, Amiga Inc told Hyperion it had violated the contract and gave it 30 days to sort it out – to finish the product and hand over the sources. This didn’t happen, so the contract was terminated  on 20 December 2006. Hyperion claims in its defence that Amiga Inc rendered the contract null through dealings with KMOS, a company which acquired the Amiga assets and renamed itself Amiga Inc over 2004-05.
Four days later, 24 December 2006, Hyperion released the final version of OS4 – although according to Amiga Inc, Hyperion claims that this was merely an update of the developers’ preview version of 16 April 2004. Since the contract ended, Hyperion had no rights to use the name AmigaOS or any Amiga intellectual property, nor to market OS4 or enter into any agreements about it with anyone else. Nevertheless, AmigaOS 4 was still being developed  and distributed. Furtermore, ACube Systems released a series of Sam440ep motherboards, which run AmigaOS 4.
For a time, the case seemed deadlocked with neither side being apparently able to prove the point either way. Without Amiga Inc‘s permission Hyperion Entertainment(Hyperion) could not use the AmigaOS name or related trademarks. Hyperion’s defence centred around the potentially contract-voiding nature of the Amiga Inc/KMOS handover, the problems they faced in acquiring the post-Commodore OS3.x source code which Amiga Inc claimed to own and have access to, and the presence of new work and open components in the new Operating System.
Hyperion Entertainment and Amiga, Inc reached settlement agreement
On 30 September 2009, Hyperion Entertainment and Amiga, Inc reached settlement agreement where Hyperion was granted, „an exclusive, perpetual, worldwide right to AmigaOS 3.1 in order to use, develop, modify, commercialize, distribute and market AmigaOS 4.x.