Free

Automotive Conservation
Interactive game for Windows or Macintosh by Ford Motors to educate consumers about both environmental issues and automotive maintenance.
http://www.automotiveconservation.com/home.shtml

Batalla Naval
Networked, multiplayer battleship game for Gnome.
http://batnav.sourceforge.net/batnav-en.html

Dara
A Windows version of the African game of Mancala.
http://www.rekenwonder.com/dara.htm

Do'SSi Zo'la
One or two player opponent blocker for Windows or Linux. [Open Source, GPL]
http://dossizola.sourceforge.net/

Expert Backgammon
Flexible backgammon game for Java with internet play and computer analysis of moves.
http://www.lpsci.com/software/html/backdesc.html

Generic Universal Boardgame
Play almost any board game: backgammon and checkers pieces are available or you can create your own. (Requires Java 2)
http://ludo.iwarp.com/

Gipf for One
Network players on Linux or Windows introduce one piece into play until achieving four-in-a-row. [Open Source, GPL]
http://gf1.sourceforge.net/

GNMM
Gnome version of Nine Men's Morris with an AI opponent, rule and board options, and support for both console and GUI play. (Open Source, GPL)
http://gnmm.sourceforge.net/

Happy End
Othello variant for Windows that allows you to play the end games of thousands of real matches played by world-level champions. Features several board designs and statistics reports.
http://www.fngo.it/happyend.asp

HB Othello
The popular board game for Windows featuring computer opponents with multiple difficulty levels.
http://www.hbteng.com/Prod06.htm

Hex
A two player strategy board game for windows in which the object is to connect two sides of the board with your tiles.
http://www.rekenwonder.com/hex.htm

KhunPhan
Includes downloads, links, and introduction for a 3D alignment game based on a Thai legend. Linux and Windows versions are available.
http://geocities.com/khunphangame/

Ludo
Customizable Windows version from India for up to four players.
http://www.geocities.com/hirak_99/goodies/ludo.html

Monopolie
Clone of the original board game Monopoly for Windows. It includes property, chance, and community chest cards as well as sound effects. [Open Source, GPL]
http://monopolie.sourceforge.net/

Mountain Vista Software
A battleship game. Contains screenshots and demo download. [Windows]
http://www.mountainvistasoft.com/

PegSol
Remove all the pegs except the last, which should be left in the center of the board. This Windows version includes a solution finder.
http://www.extrabit.com/freestuff/

Qianhong Xiangqi
Includes screenshots and downloads. [Windows]
http://www.angelfire.com/oz/xiangqi/

Shogi Variants
Windows program to play the Japanese member of the chess family of games or one of 16 other ancient and modern Shogi variants.
http://www.netspace.net.au/~trout/

Space Monopoly
A simple logical game of buying and selling shares. Requires Windows.
http://space.monopoly.iwarp.com/

Valvo
Board game for Windows in which you race an opponent and try to block her good moves by opening and closing valves.
http://familygames.com/free/valvo.html