Rules
Players take turns placing one or two adjacent pieces (cubes) of their colour on valid empty points of the 6x6x6 board area. A point is valid if it is: 1) a board point, or 2) supported by an existing piece. Players may not place a piece directly upon an enemy piece unless that move extends an existing friendly group.
Only one piece may be placed on the opening move.
All pieces in a stack are owned by the player with the topmost piece.
Connection: Two stacks of the same colour are connected if they are squarely adjacent to each other. A group is a visibly connected set of stacks.
Freedom: A stack has freedom if it is adjacent to at least one empty board level point. A group has freedom if at least one of its member stacks has freedom.
Surround capture: After playing a piece, all enemy groups without freedom are captured and removed from the board. All pieces in captured stacks are removed, regardless of their colour.
No suicide rule: It is not permitted to place a piece without freedom, unless that move captures neighbours to create its own freedom.
Ko rule: It is not permitted to repeat a previous board position (this has not been implemented so is up to the players' discretion).
Players may not voluntarily pass, but are forced to pass if there is no legal move.
The game ends when neither player can make any further move. Players' scores are given by the total height of the stacks that they own; the player with the highest score wins.
Multiplayer: Multiplayer Drogo is played using exactly the same rules as the two-player version.
Examples
An X piece at 'a' captures the O group, which has no remaining freedoms. + + + + + + + + + +
| |
| +-----+ |+-----+-----+
+ /| x x | + + /| X X x x | + +
| a || x x | || X X x x |
|+-----+-----+-----+ |+-----+-----+-----+
/| o o o o | x x | + /-----/-----/| x x | +
|| o o o o | x x | | || x x |
|+ + + + | |+ +
/| o o o o | x x | + + + /| x x | +
|| o o o o | x x | | || x x |
|+ + + + | |+ +
/| o o o o | x x | + + + /| x x | +
|| o o o o | x x | | || x x |
|+-----+-----+-----+ | |+-----+
/-----/-----/-----/-----+ +-----+-----/-----/-----+
If instead it is O's turn, O can delay this group's capture by building over the surrounding X pieces to create another freedom. + + + + + + + + + +
| |
| +-----+ | +-----+
+ /| x x | + + + /| x x | + +
| b || x x | | || x x |
|+-----+-----+-----+ |+-----+-----+-----+
/| o o o o | x x | + /| o o o o | x x | +
|| o o o o | x x | || o o o o | x x |
|+ + + + |+ + + +
/| o o o o | x x | + /| o o o o | x x | +
|| o o o o | x x | || o o +-----+-----+
|+ + + + |+ /| o o o o |
/| o o o o | x x | + /| o o || o o o o | +
|| o o o o | x x | || o o |+-----+-----+
|+-----+-----+-----+ |+-----/ / /
/-----/-----/-----/-----+ /-----/-----/-----/-----+
Notes
Since the board space is cubical, players should be aware that there is a strict limit on how high pieces can be stacked; vertical ladders are doomed to failure.
Some multiplayer Go variants relax the connection definition so that enemy groups may consist of stones of any colour except the current player's. Drogo maintains the stricter definition - that any group may only consist of one colour - to encourage captures.
History
Drogo rules copyright (c) Cameron Browne, March 2006.
Thanks to Phil Bordelon for suggesting the "topmost player owns the stack" rule, which solves a lot of problems with hidden pieces.
The name "Drogo" refers to the fact that the game combines Druid-like equipment with a Go-like ethic (the more obvious "Drugo" sounded too much like a William S. Burroughs novel).
Implementation and Help file by Cameron Browne, March 2006.