Naval Battle (KBattleShip) is a fun battleship game built on the KDE libraries. It can be played single player or multi-player over the network as long as you've got a friend willing to play (there is no central game server).
Brief history lesson
KBattleShip was created in 2000 by Nikolas Zimmermann and Daniel Molkentin who maintained for years. It was re-written for KDE4 by Paolo Capriotti in 2007. It was later renamed to "Naval Battle".
Plot and Gameplay
If you don't know how Battleship works: You place your ships on the battlefield, the enemy shots at you and you tell the adversary if they hit something or not. Then it's your turn to shoot and hope you hit one of his ships. The one who hits all the enemy's ships first wins.
It's kind of fun - and more importantly, you can play it anywhere (Battleship, not Naval Battle which requires a computer): All you need to do is to draw a board and name the vertical rows A B C, and the horizontal rows 1, 2 3 - so you can play it anywhere as long as you have a pen and a math-book (or any other piece of paper which is already full of squares).
Naval Battle is like you'd expect a battleship game to be. It's a battleship-game. You place your ships and blindly shoot at the enemy. That's it.
It's fun for a few rounds. Then it gets old.
The MultiPlayer support
Naval Battle lets you to connect to a known friend who's ready to play. There is no central server so you have to ask a known party to play. You or your friend starts the game in "server" mode and the other person connects. No central server or match-making limits it's usefulness. Still, it is a feature which can be used if you have a friend ready to play.
Naval Battle's homepage is at https://games.kde.org/game.php?game=kbattleship