AmigaOS is the proprietary native operating system of the Amiga and AmigaOne personal computers, introduced with the launch of the first Amiga, the Amiga 1000, in 1985. The most recent release is AmigaOS 4.1, developed by Hyperion Entertainment, which received in 2009 by Amiga Inc. an exclusive, perpetual, worldwide license to AmigaOS 3.1 in order to develop and market AmigaOS 4 and subsequent versions. AmigaOS is a single-user operating system based on a preemptive multitasking kernel, called Exec. It includes an abstraction of the Amiga's hardware, a disk operating system called AmigaDOS, a windowing system API called Intuition and a desktop file manager called Workbench. A command-line interface, called AmigaShell, is also integrated into the system, though it also is entirely window based. The CLI and Workbench components share the same privileges. Notably, AmigaOS lacks any built-in memory protection. AmigaOS is formed from two parts: a firmware component called Kickstart and a software portion usually referred to as Workbench. Up until AmigaOS 3.1, matching versions of Kickstart and Workbench were typically released together. However, since AmigaOS 3.5, the first release after Commodore's demise, only the software component has been updated and the role of Kickstart has been diminished somewhat. Firmware updates may still be applied by patching at system boot.

In 2006 AmigaOS 4.0 was rewritten to become fully PowerPC compatible. The screens became draggable in any direction, drag and drop of Workbench icons between different screens was possible, new version of Amidock, TrueType/OpenType fonts and movie player with DivX and MPEG-4 support were added. In AmigaOS 4.1, a new Start-up preferences feature was added which replaced WBStartup drawer. Additional enhancements were a new icon set to complement higher screen resolutions, new window themes including drop shadows, AmiDock with true transparency, scalable icons and AmigaOS with auto-update feature.