Battle.net

Battle.net is an online gaming service provided by Blizzard Entertainment responsible for hosting StarCraft multiplayer games and related services. It was launched in January of 1997 with the release of Blizzard's action-RPG &mdash; 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.

Features
With the release of StarCraft in 1998, usage of the Battle.net service increased significantly in comparison to Blizzard's previous games. Features such as ladder ranking and game filters were added to the service. Battle.net grew even larger after the release of the expansion pack StarCraft: Brood War. Concurrent player counts and games played reached the tens of thousands. This was especially evident in South Korea where StarCraft became a runaway hit and concurrent player counts on Battle.net would often be many times what they were in the United States.

StarCraft also brought with it a new copyright protection scheme using CD keys. Under Diablo, Battle.net would allow anyone who had a copy of the game to connect to the service. This allowed people who pirated the game to play on Battle.net. With StarCraft, only those players who had a valid CD key were allowed onto the service. A StarCraft CD key is a generated 13-digit number that could either be muted (unable to chat), voided (restricted to channel 'The Void'), banned (disabled usage), or usually working (no restrictions). In addition, only one person can be connected to Battle.net service using a specific CD key at a time. Every Blizzard game since StarCraft has required a unique, valid CD key to connect to Battle.net (excluding Starcraft: Brood War, Starcraft's expansion which was also released in 1998). With the release of the Gateway system in Broodwar, two players can play at the same time, as long as they are on different gateways, though they cannot play in the same game, chat with each other, etc.

Growth history
Blizzard claims "millions of active users" on Battle.net, and that they are the leaders of online gaming, noting that even Xbox Live doesn't even come close. By November 1997 they had 22 million games played, 1.25 million different users, and that they averaged 3,500 new users each day. By April 1999, it was reported that Battle.net had 2.3 million active users, and more than 50,000 concurrent users. By September 2002, their active user count had jumped to 11 million. By September 2004, their active user count was up to nearly 12 million, spending more than 2.1 million hours online each day, and they had an average of 200,000 concurrent users, with a peak concurrent user count of 400,000.

Community
A community of developers has arisen around Battle.net. Many unofficial clients are available for Battle.net, and most of the protocol used by Battle.net-enabled games has been reverse-engineered and published by volunteers.

Also, several communication tools have been made, like a "whisper" tool, so that you could talk to your friends even if they were in a game