Although Battlefield: Pirates actually does kinda exist in the form of mods for Battlefield 1942 and Battlefield 2, this game, BlackWake, will probably surpass either of those. Provided it's finished.
What we're looking at is a multiplayer team-based shooter for PC, centred around naval battles. Here's a video describing the game's features; basically, it will be exactly like this, except not janky. Because, you know, alpha. It's a concept trailer, and the game only started development last year.
Note the setting. It's the 18th century, meaning it's a four-way battle between the British, French, Spanish and pirate fleets. It's like the multiplayer mode Assassin's Creed IV never had, and you even get to watch your ship sink from the inside. That is, again, if the game gets finished.
BlackWake: Dead Marque is coming when it's done, and has a YouTube page filled with commentated footage, along with an IndieDB entry where you can gawk at screenshots, and a Greenlight concept page where you can give feedback.
BlackWake: Dead Marque [IndieDB]