Go (game)
The playing pieces are called "stones". One player uses the white stones and the other, black. The players take turns placing the stones on the vacant intersections ("points") of a board. Once placed on the board, stones may not be moved, but stones are removed from the board if "captured". Capture happens when a stone or group of stones is surrounded by opposing stones on all orthogonally-adjacent points. The game proceeds until neither player wishes to make another move. When a game concludes, the winner is determined by counting each player's surrounded territory along with captured stones and komi (points added to the score of the player with the white stones as compensation for playing second). Games may also be terminated by resignation. A teacher might simplify the explanation by saying to a student "you may place your stone on any point on the board, but if I surround that stone, I will remove it."
TwixT
Twixt is played on a board comprising a 24×24 square grid of holes (minus four corner holes). The playing pieces are pegs which fit the holes, and link pieces which join pegs along the diagonal of a 3×2 grid. In the 3M edition, players are Red and Black; different sets may use different colors. The topmost and bottommost rows of holes belong to the lighter color; the leftmost and rightmost rows to the darker color.TwixT has been proven to be PSPACE-complete for determining the game value, via a reduction from Hex. TwixT has also been shown to be NP-complete for whether a single set of vertices can support a connecting path, via a reduction from 3-satisfiability.
These proofs are indicative of a complex strategy: the game has not been solved, no winning strategy has been discovered, nor is the outcome of the game with perfect play known.
On the 24×24 grid, tactical considerations tend to predominate. The opening phase is over quickly, and the rest of the game is spent attempting to tactically execute the plan. Hex, which has a very similar game object, may have more predictable tactics, but strategical considerations are much more important. In this sense, Hex is more like Go than TwixT, since a single move is generally less committal, and consequences may take longer to play out.