Nostalrius
Nostalrius was a private World of Warcraft server created in 2015. The server featured a version of the game called "Vanilla", or, one of the first versions of the game (Version 1.12). The server host received a Cease and Desist letter from Blizzard Entertainment and so the server was shut down on April 10, 2016, leading to unprecedented protests on Facebook and Twitter and large scale coverage in mainstream computing journalism.
It was one of the most successful private servers to date, with over 800,000 accounts registered and 150,000 active accounts. Since the conclusion of Nostalrius servers, a discussion about the possibility of Blizzard opening "Legacy" servers has begun.
Discussion of legacy servers
One of the biggest discussions on legacy servers came out of the entire Nostalrius issue. A petition on change.org has received over 200,000 signatures pleading Blizzard to hear the voices. Many famous Youtubers have made videos on this very topic discussing the pros and cons of Legacy servers, and it managed to get the attention of one of the original designers of World of Warcraft, Mark Kern, who supports the idea of Legacy servers. Blizzard Entertainment was silent on the issue until April 25, where the lead game developer responded to the discussion.
Blizzard's Response
On April 25, 2016, A Blizzard employee responded to the Nostalrius discussion. He spoke of the possibility of "Pristine" realms, with many of the new features in the game turned off, to make leveling harder, and social interaction more prevalent in the game[1][2]
Further Developments and the Return of Nostalrius
After a month or so of large scale protests, Blizzard invited the Nostalrius team to the Blizzard HQ, to present the case for Vanilla. In the six months following, Blizzard did not respond at all to any communication from the Nostalrius team, and then Blizzard announced they would not be making any statements about Vanilla the annual BlizzCon convention. Consequently, the Nostalrius team released their source code to Valkyrie WoW, another long-standing private Vanilla WoW server, hosted in Russia, and the Nostalrius servers will before the end of 2016 return, with the player database as it was just before the shutdown in April.