Copyright (c) 1991 Reiner Knizia, Pro Ligno Spielewerkstatt

This game is played on an empty 7x4 square board:

TURNS - On each turn, each player must do one of the following actions:
Drop a friendly stone on a column's lowest possible empty cell (the lowest row is the bottom row).
If the column is full, insert a friendly stone on top and shift all stones down, removing the bottom stone.
GOAL - A player wins by making a (orthogonal or diagonal) 4 in-a-row.
However, if both players have a 4 in-a-row, the game continues.
A dropping example

The green dots show the possible drops of the next player. 

A shift example

Black's turn. If Black shifts the full column, all those stone move one line down and the marked white stone if removed. A new black stone appears at b7. 

After the slide, both players will have a 4 in-a-row, so the game continues until at least one of those 4 in-a-rows disappear. Probably, White should shift that column again, since he has a majority of white stones there, and the sequence of shifts will get him a winning position.