Quad is also a board game for two players, invented by G. Keith Still. It is played on a square 11 by 11 board, with the 4 corner squares out-of-bounds (leaving 117 playable squares). One player plays 'Black', the other player plays 'White'.
Each player starts with 20 attacking pieces (of the player's colour), called 'marbles', and 6 blocking pieces (colour irrelavent), called stars. Players take turns moving.
A move consists of a player placing one or more stars in blank squares, then placing one marble in a blank square. The winner is the first person who forms a 'quad', a perfect square with their coloured marbles at the corners. The game ends as soon as there is a winner, or it ends in a draw if neither player wins before all the marbles are played. It is important to realise that the quads need not be lined up with the grid of the board: for example, if you start at one marble, there's another 3 squares right and 2 squares down, another 3 squares down and 2 squares left from the second, and another 3 squares left and 2 squares up from the third; this is a valid quad. A diagram will show this better:
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It's quite an involving game, and quite difficult to play. Trying to form quads is easy, trying to keep your opponent from forming quads is more difficult, and as you play against a more skilled opponent keeping enough stars to stay in the game is very hard.
One fairly obvious strategy is to put three marbles in a straight line, evenly spaced, then placing one on a perpendicular to make a sqaut 'T'-shape; unless your opponent has already played in one of the squares, you have three possible winning moves: complete a square in the bottom-left of the 'T', complete a square in the bottom-right of the 'T', or complete a diamond centred on the join of the 'T'. If those three squares are empty when you place your last marble, your opponent must use at least two blocking stars (unless they have a winning move at that point). Continue with tricks like this, and if you're a better player (and/or a luckier player) then your opponent will run out of stars before you; then, your next trick could win the game. (Of course, there's also the possibility of simple oversights; neglecting to block an opponent's quad - and this can happen quite a bit too, the board gets quite busy very quickly, and a person can simply not notice a 3/4-quad until too late.)
I have an application on my Psion 5mx, written by Ewan Spence, which allows me to play Quad against the computer, it includes a help file with the following quote from G. Keith Still:
I developed the game of Quad back in 1979 when I was a student at university. My goal was to develop a quick-to-play but complex game with fewer rules than Go. My friends and I at Robert Gordons Institute of Technology in Aberdeen, Scotland played hundreds of games together. It was as a result of these many trials that I came up with this final version of Quad - the 11*11 board, 6 blocking pieces, etc..
I associate Quad with those carefree times when pressure was an exam and life was one long summer day - and with my friend Graham "Ibrox" Mackenzie, who is no longer with us. He and I spent many lunchtimes playing Quad at the Student Union. He was the master of the "Shooting Star" strategy and shall be fondly remembered.
The original board for Quad was handcrafted from chipboard, and we'd often have disputes about whether a declared quad was really a square. We tried using an L-shaped piece of plastic as a guide, but it didn't always help. We even resorted to elastic bands, but that didn't always help, either. Games could often go the distance only to find that a player had won ages ago. Try the game without the benefit of the computer declaring the winner and you'll see what I mean.
In 1980, a technician at the school made me a small clear plastic board on a machine tool. It was perfect; it fit in the pocket and used nice small pieces. At last we had a game we could really play. He said "If it ever makes you a million, buy me a box of Havana cigars." I guess he'll still be waiting, but I'm happy that now, after all these years, others will get the chance to play Quad.
Quad remained in a box in my desk gathering dust until a chance discussion with my doctoral dissertation advisor, Professor Ian Stewart. Ian thought it would make a good article for his regular slot in Scientific American. Michael Mefford saw the article in Scientific American, and thought a computerized version of Quad would make a good Utilities column for PC Magazine.
Michael has done a great job with Quad for the PC and now Ewan has done an equally great job for my Psion. Quad is, once again, back in my pocket on a small piece of plastic.
I hope you enjoy playing it as much as we did back at the university.