It uses Chinese rules, with two simple exceptions:
1. Enclosing a region captures all enemy stones within.
2. It is illegal to play in a region enclosed by the enemy.
If black plays at the square, then all the white stones are captured, and it becomes illegal for white to play within the enclosure.
Clarification: you can enclose enemy stones using the wall, but only if you have a shape that either (1) touches same wall twice, or (2) touches two adjacent walls. This prevents someone from capturing the entire board by simply building a bridge between opposite walls. If that were the case, then the game would be Hex, not Go!
Clarification: you can play in an "illegal" space if and only if it leads to immediate capture of enemy stones (just like in normal Chinese rules).
Herman What happens if a player connects two diagonally opposite corners? :)
ChrisBandy Lol he would capture the entire board. So I guess the first two stones of the game will always be placed in opposite corners. That's...joseki, right? Lol
But anyway, you can see why I abandoned this version! :)