Serenity
Serenity is a CCP server cluster that exclusively serves EVE Online's Chinese player base and hosts an entirely separate instance of the EVE Universe that is not normally influenced by activities on Tranquility. It is one of three production server clusters that CCP operates, alongside Tranquility. Accounts on this server are specific to the cluster, and cannot interact with players of other server clusters, much like how actions on Singularity do not affect those on Tranquility.
Due to the separation of players between the two production server clusters, there are separate characters, corporations, and alliances between the two, and while some corporations and alliances share a presence on both server clusters, they are separately managed. Sovnull on Serenity is also in a different state at any point compared to the state of sovnull on Tranquility, with different alliances holding different systems and regions.
Serenity and Tranquility have occasionally interacted with each other. During the Triglavian Invasion (Chapter 3), the results of the invasion on each server affected both. Fanfest 2015 featured a tournament between champions from both servers[1][2]. Additionally, SKINs are normally synchronized and added to each server's database at the same time even if they won't be available on both [3].
CCP has a second Chinese server, Infinity, with a different map and game mechanics than either Tranquility or Serenity.