Copyright (c) 1978 Alex Randolph, Lakeside Publ. 

This game is played on a 6x6 square board, with one of these possible setups :

TURN - On each turn, each player may push one of his stones in any direction and any distance in a straight line provided that he pushes one or more of the opponent's stones Overboard.
A player may push stones Overboard even when there are gaps between stones or between stones and the edge of the board.
He can not push his own stones Overboard. 
If he can not or do not want to push his opponent's stone(s) Overboard, he may push one of his stones only one space to the next empty cell.
GOAL - The player with the last stone on the board, wins.
An example

White started and pushed to the left, both a4 and c4 with his marked stone.

Some strategy tips from the original ruleset (thanks to Peter Loop):

Early in the game look for rows where you can push off a large number of your opponent's pieces.
Try to leave your pieces between your opponent's pieces. By doing so they are safe.
Try to avoid setting up rows with a large number of your pieces.
Towards the end of the game, be careful about leaving your pieces in a row.
Even if both players each have only one or two pieces, someone can win.