If you have a copy of Total War: Shogun 2 and/or its expansion Fall of the Samurai and posess mad map editing skills, the Total War Battle Map Editor has just been released.
With this handy tool you can make and share Land, Naval, and Siege Battle maps with others and use them in Single player Custom Battle Mode or Multiplayer.
To get started, boot Steam and check the Tools menu.
Going along with the editor launch, there's also a game update which improves multiplayer functionality and squashes a load of bugs. Hit the source if you want full details.