From Mr. de Bono's website:
The intention was to produce the simplest possible game that could be played with a high degree of skill. An attempt was made to fulfill the following conditions:
1. A minimum number of playing pieces, preferably one each.
The smallest possible board.
2. A game with very few rules, one that would be very simple to learn and play.
3. A game that could be played with a high degree of skill.
4. A game that would not be determinate. A determinate game such as nim or noughts and crosses, is one in which the starting player could always win if he knew the strategy. An indeterminate game is one which two perfect players would play forever.
The L game was the result. Each player has only one piece. The board is four squares by four squares.
Appears with 3 SPOT game in Rex Games' Two Smart Games mini-anthology.