Sea of Thieves is a new title from Microsoft and Rare. It’s a multiplayer pirate game set in a shared world. This means you’ll share ships and battles for loot with other players. Destiny comes to mind; except with pirates.
There’s scarce other details from either E3 or the press releases since. The game will be for the Xbox One. There’s no release date yet. Rare is a British company responsible for Wizards & Warriors and Battletoads before striking a deal with Nintendo to help with the like of Golden Eye 007 and Perfect Dark. Microsoft bought them in 2002.
There’s an official Sea of Thieves site with a sign-up form for more information.