The first widely acknowledged private server appeared for Ultima Online, while the retail version was still in beta. An open source tool was released which allowed players to play without connecting to the Ultima Online server.
From this tool, several private server emulators spawned. Ultima Online now has many private servers, known as ‘Free Shards’, with enough customized content to rival the retail servers.

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Older private servers for games like Ultima Online and Ragnarok Online have existed, with an active player base, for several years. Private servers are still being developed for recent games. Aion Online, released in 2009, has an emulator released and several private servers already exist.