[I come up with ridiculous ideas]
http://www.youtube.com/watch?v=st05w1jYIdQ
So this is a concept that developed out of a 2D online space trade idea that turned out to be too awesome to produce.
The Story
Global warming causes the ocean to rise and only the human resources department at the top of your office block survived! You realise your childhood dreams of becoming a pirate can finally come true, so you wear that neck-tie round your head, unbutton your shirt and take the plunge into the vast, vast, vast ocean.
The Gameplay
The game is online, multiplayer. Each server is an office block in the middle of the ocean that survived the freak global flood. When a player first joins a server that have to decide on a flotation device to use at their initial boat, things like water coolers, desks, computers, pot plants or even the decorative anchor that seems to be nailed to the far-east wall of the office.
When you're in the water you're free to do anything, the office will contact your on the radio asking for you to find resources such as treasure, food, fresh water, anything, and it's up to you to find them, be it steal them from other players, find them legitimately or you could abandon your company entirely and make your own band of pirates.
Each ship(?) type has it's own health, speed and how much water it takes on per kilometer, you can also get a compass that points north, a telescope to see in the distance or a nice flag to tell you wind direction, it's all about navigation, trade and piracy. Arr!
Ships have their own environment too, so players can take control of their little guy and jump onto another ship and push the occupants off, or you can tie up and jump back into that flooded office block you used to work in and take another water cooler.
What will it be like?
I suppose it would be a cross between the Crimson Permanent Assurance and Water World.
There will be day/night cycles as well as weather, I have plans to add seagulls that fly near land and various fish that attack you.
Killing albatross' is always bad luck.
Here's a dev screen:

I just want to be a pirate.