Liquid War 6 is a unique multiplayer wargame. Your army is a blob of liquid and you have to try and eat your opponents. Rules are very simple yet original, they have been invented by Thomas Colcombet. It is possible to play alone against the computer but the game is really designed to be played with friends, on a single computer, on a LAN, or on Internet.
An older version, Liquid War 5, is available, but is not part of the GNU Project. Only Liquid War 6 is part of the GNU Project, it is a complete rewrite.
The official page of Liquid War 6 is http://www.gnu.org/software/liquidwar6/. For more information, you can read the Wikipedia article about Liquid War.