My Best Game (I Suspect): Ketchup

Ketchup was a finalist for the Thousand-Year Game Design Challenge

Ketchup is a simple, drawless game with a devilish dynamic. The goal is to end up with the largest group of stones on the board, but as you get closer to winning, your opponent gets more powerful. Whereas most stone placement games are about position, Ketchup is about timing, position, and the interplay between them.

It's for two players, played with black and white stones on this initially-empty board:

Terminology

Group – a set of connected, like-colored stones on the board.
Group Size – the number of stones that a group contains. The smallest possible group contains 2 stones. The figure below shows three groups with sizes 2, 5, and 11.
To Drop- to place a stone on any empty space.

The ovals around the board are called the scoring track. Before the game starts, set aside one white stone and one black stone. These will be moved along the scoring track as the game goes along to mark the size of each player's largest group.

Rules

One player owns the white stones and the other owns the black stones.
White begins by dropping 1 stone. From then on, starting with Black, each player must drop 1 or 2 stones on her turn.
If the largest group on the board (regardless of color) is larger at the end of your turn than at the beginning, your opponent may drop up to 3 stones on her next turn.
The game ends when the board is full. The player with the largest group wins. If the players’ largest groups are the same size, compare their second-largest groups, and so on, until you come to a pair which aren't the same size. Whoever owns the larger of the two wins.

Here's an article covering basic strategy.

You can play online, in realtime games against human opponents here:

You can also play turn-based Ketchup at Christian Freeling's site for abstract games, Mindsports.

Here's a printable pdf board with a green scoring track, for playing Ketchup with full-size Go stones (it's 15x16 inches so you'll have to print it at a printing store if your printer can't handle oversized jobs. Alternatively, you can use a free program called Posterazor to print segments of the board onto multiple standard sheets such that they can be combined to construct the full-size board):