.hack (pronounced "dot-hack") is a Japanese multimedia franchise that encompasses two multimedia projects: Project .hack and .hack Conglomerate. Both projects were primarily created/developed by CyberConnect2, and published by Bandai. The series is still ongoing, with a new manga series recently announced.
The plot of .hack is set in the early part of the 21st century. In this world, the Internet has spread across the planet, creating a unified global network which controls everything from the stock market to vending machines. At the center of this network is a popular virtual-reality massively multiplayer online role-playing game (MMORPG) called The World. Players from all around the world play this game, which has been made available in over 20 different languages. However, problems begin to arise when players begin mysteriously falling into comas while playing the game. Each part of the .hack series gives the viewer a different piece of the mystery of The World, which when put together explains what is actually occurring within the game.
Each project, Project .hack and .hack Conglomerate, is set in a different part of The World's history. Project .hack occurs in the original game The World and .hack Conglomerate takes place in its sequel, The World R:2. Both stories are related, and share common themes and characters.