The history of iTunes:
2001 - version 1 was released. Simple design based on the Soundjam code.
version 1.1.1 - Mac version is released
version 2.0 Oct 2001, Original iPod is now supported, CD burning is improved and equaliser/cross fader.
Version 3.0
Version 4.0 April 2003, Music store support is added. DVD burning
Version 4.1 Oct 2001, Voice notes and on-the-go playlists are added. The first windows version is released.
Version 4.7 iPod photo support added. October 2004. Multimedia makes its way through Itunes.
Version 4.8 May 2005, Video support added. Support for international music stores. Some security improvements also made. iTunes is now fully globally compatable.
Version 4.9 is released. June 2005. Podcat functionality is added.
Version 6.0 - Video transfer functionality is added to support the 5th generation iPod classic.
Version 7.0 - New look
Version 7.1 - March 2007. Support for Apple TV.
Version 7.3 - June 2007 - iPhone activation and syncing support is introduced.
Version 7.6 - January 2008 - Movie rentals via the iTunes store is added.
Version 8.0 - The new Genius content-suggestion feature is added along with the new grid view and tv shows in HD. (Links to WEB 3.0 participatory culture, information is taken from YOUR playlist and redirected to sell you things). This is one of the first examples of Mac using web 3.0.
Accesability/Platform(s)
Multimedia support such as photos and videos with sharing support to the iPod and iPhone, MP3player, etc. The iTunes store itself is mainly available from your main computer, but there are also ways to access the store and purchase items from modern phones with web connections. It does not require internet access to listen to the sounds over and over, on multiple devices as they are functionable for transfering the songs.
Rivals
Spotify - supplies music in a similar way to itunes, in a similar looking player. The player however uses constant internet streaming access, which does not benefit the user to transfer music via other applications and equipment, or transport it.
Web based players also offer similar services, free however these also require an internet connection to permanently use, unless items are purchased for MP3. Example: Last.fm, We-7.
Media variety, Availability, Convergence:
Photos
Songs (MP3)
Videos
All purchasable from the itunes library and with support to transfer them to other hardware such as Ipod, iPhone, MP3, your computer, etc.