ITunes

iTunes is Apple's music and video management software. It also serves as a desktop client for the iTunes Store and handles iOS device synchronization.

It consists of two major components: iTunes itself, and Apple Mobile Device Support (AMDS). Apple Mobile Device Support is the component responsible for synchronizing with iOS devices. Previous versions included QuickTime, which was used for media playback.

From version 9 to 12.10.8.5, iTunes on Windows includes a component called Apple Application Support, which includes WebKit and some other Apple libraries and tools. It is used to display the iTunes Store, as well as iTunes LPs and iTunes Extras.

Early
iTunes was initially released for Mac OS 9 on 2001, having been derived from the SoundJam MP codebase Apple had acquired from Casady & Greene. iTunes was first released for Mac OS X on 2001 with version 1.1, and it became a built-in app with the release of Mac OS X 10.1.

iPod, iTunes Store, and Windows
Alongside the launch of the iPod on 2001, iTunes 2.0 was released to provide its syncing functionality.

The iTunes Store was launched on 2003 with the release of iTunes 4.0. Notably, iTunes 4.0 was the first version to support the AAC audio codec, used by all music purchases from the iTunes Store.

On 2003, iTunes 4.1 was released, being the first version to support Windows.

On 2004, iTunes 4.5 added support for the Apple Lossless (ALAC) audio codec.

On 2004, iTunes 4.6 added support for AirPlay, then known as AirTunes.

On 2006, iTunes 6.0.2 added native support for Intel Macs.

On 2006, iTunes 6.0.5 added support for Nike+iPod.

On 2007, iTunes 7.1 added support for the Apple TV (1st generation).

iPhone
Coinciding with the launch of the iPhone on 2007, iTunes 7.3 was released with support for activating the device, and syncing a music library to it.

On 2007, iTunes 7.4 added support for the newly-launched iPods, including the iPod touch, iPod classic (6th generation), and iPod nano (3rd generation).

Coinciding with the launch of the iPhone 3G, iPhone OS 2.0, and the App Store on 2008, iTunes 7.7 was released with support for the new device, and for downloading and syncing .ipa-packaged apps from within the iTunes Store section of the app. The Remote app was also released.

Coinciding with the launch of the iPad and iBooks on 2010, iTunes 9.1 was released with support for the device, including downloading and syncing books from the iBooks Store.

Coinciding with the launch of the Apple TV (2nd generation) on 2010, the first Apple TV to run a variant of iOS, iTunes 10.0 was released with support for the device, additionally introducing the iTunes Ping social network.

iCloud & Apple Music
Coinciding with the launch of iCloud and iOS 5 on 2011, iTunes 10.5 was released with support for Wi-Fi Sync and iTunes in the Cloud. Notably, QuickTime was no longer bundled with the iTunes installer on Windows.

On 2011, iTunes 10.5.1 added support for iTunes Match.

On 2013, iTunes 11.1 added support for iTunes Radio.

Coinciding with the launch of Apple Music on 2015, iTunes 12.2 was released with support for the service.

On 2017, iTunes 12.7 removed support for browsing, downloading, and synchronising apps from the App Store, including the "Applications" tab that provided a desktop view of the device's home screen. It additionally removed support for ringtones, and entirely discontinued support for synchronisation or streaming content to Apple TV (1st generation). Due to the major feature removals, the iTunes 12.6 branch continued to receive updates, starting with 12.6.3.6 on 2017, and ending with 12.6.5.3 on 2018.

On 2018, iTunes 12.8 added support for AirPlay 2.

On 2018, with the release of iTunes 12.9, Apple's release strategy for iTunes on macOS changed to no longer treat it as a separately upgradable component. This and all future versions were exclusively bundled with macOS Mojave, and cannot be downloaded as a .dmg nor installed on prior versions of macOS, as had been possible up to this point.

Post-iTunes
As of macOS Catalina, iTunes has been replaced by separate Music, Podcasts, TV, and Books apps, with iOS device functionality merged into Finder. iTunes 12.9.5.5 is the final release on macOS, bundled with macOS Mojave 10.14.6 Supplemental Update (Build 18G95).

Additionally, since at least macOS High Sierra (possibly as early as the introduction of System Integrity Protection in OS X El Capitan), Apple Mobile Device Support handles its own updates. When a device unknown to the currently installed build of AMDS is connected, MobileDeviceUpdater.app prompts the user to install a software update. Previously, AMDS would only be updated by installing a full iTunes or Xcode update.

iTunes is still in use on Windows, however it is soon to be replaced by the Apple Music, Apple TV, and Apple Devices apps, currently in preview.

Mac OS 9
Initial versions of iTunes supported Mac OS 9. Support was dropped with version 3.0.

macOS
Mac OS X support was introduced with iTunes 1.1.

64-bit
With iTunes 7.6, Apple introduced a 64-bit edition of iTunes.

iTunes 7.3 for Windows 2000
For a brief period, Apple released separate iTunes downloads for users of Windows 2000, before discontinuing support for Windows 2000 entirely. These releases lack Apple Mobile Device Support, meaning iOS devices are not supported.

Older video cards
With iTunes 12.1, Apple bundled 64-bit versions of Apple Mobile Device Support and Apple Application Support with iTunes. For iTunes 12.1 through 12.4.3.1, Apple also offered a version for 64-bit Windows computers with older video cards, which keep the 32-bit versions of said libraries. Installing this version is necessary when using a 32-bit program expecting 32-bit libraries, such as many older jailbreak/jailbreak-related tools.