Boulder field is a two-player game. Players are trying to connect four or more of their pieces in a row.
Pieces can be inserted into the field from any four directions and they always fall all the way to the opposite side, stacking other pieces to tight rows on their way.
This makes the play field change dynamically on every turn.
If four or more pieces of the same color are connected in a row they will turn into immovable solid rocks.
The game runs on one device in a traditional board game fashion, sharing the device's screen for both players.