Wikipedia
Battle.net is an internet-based online gaming, digital distribution, and digital rights management platform developed by Blizzard Entertainment. Battle.net was launched on November 30, 1996, with the release of Blizzard's action- role-playing video game Diablo.
Battle.net was the first online gaming service incorporated directly into the games that make use of it, in contrast to the external interfaces used by the other online services at the time. This feature, along with ease of account creations and the absence of member fees, caused Battle.net to become popular among gamers and became a major selling point for Diablo and subsequent Blizzard games. Since the successful launch of Battle.net, many companies have published online game services mimicking Blizzard's service package and the user interface.
Blizzard officially unveiled the revamped Battle.net 2.0 on March 20, 2009. It later revealed further details of the Battle.net revamped features at Blizzcon 2009 which supported StarCraft II, Diablo III and World of Warcraft. The original Battle.net was then renamed to Battle.net Classic.