Copyright (c) 1996 Kris Burm

GIPF is played on the following initially empty hexagonal board. 
Each player starts with 18 stones in reserve.

GIPF - A GIPF stone is two stones stacked one upon the other.
GIPF PHASE - On each turn, each player may insert one GIPF piece thru a board edge on a given direction. If there is one stone there, it is pushed to the next cell on that direction, and if it goes to another occupied cell, this one is also shifted, and so on... 
A insertion in a full line (meaning that another insertion would mean that the last piece would go offboard) is not allowed.
STONE PHASE - When a player inserts a single stone (using the same method), he cannot insert more GIPF stones.
CAPTURE - When, after a insert, there is one or more lines with 4 adjacent stones (single of GIPF) of the same color, all the adjacent stones of that line (of either color) are removed from board. The stones of the player's color go back to reserve, the others are captured.
This does not count has a move. E.g.., i after white's move, black must remove a line of his stones, he still inserts a stone on the next move.
If two lines of 4 are created and they do not intersect, both must the removed. However, if they intersect, the player chooses what line to remove.
The player that removes the line, if he wishes, may keep the GIPF pieces (of either color) onboard. If he removes them, they are split into two stones.
GOAL - The player with no more stones in reserve or with no GIPF pieces onboard, looses.

Some remarks from the author: 1. Don't misinterpret the aim of the game; you can only win by capturing the opponent's pieces, not by returning your own pieces repeatedly from the board to the reserve! 2. A tie is not possible. The first player to run out of pieces loses the game, even if the other player, too, would run out of pieces in his next turn. 3. Players should always be able to see how many pieces the opponent has left in his reserve. Leave them clearly visible next to the board.

An example

White started by placing a GIPF piece at a3, then Black insert at the same cell at east direction, pushing the white GIPF one cell.

Lines of 4

Black inserted a piece at d1 (the red stone) at SE direction, pushing 4 stones on the same direction. There is now a line of 4 black pieces. The Black player must remove the 3 single stones and decide to remove or not the black GIPF, but it cannot capture the other two stones on the same line, since they are not adjacent to that line of 4 (there an empty cell in-between at b4).

You can play GIPF at Rognlie's PbM server. There is also a program (for Linux and WIndows) called GF1 that plays the game. More information can be found at the GIPF project website - GIPF it's the 1st game of a series of 6.