Trioncube looks a bit like Tetris, and initially it plays that way too. A rectangular play area takes up most of the touch-screen, and into this various shapes descend, each comprised of three blocks rather than the standard four (come in Alexey Pajitnov, your time is up). Unsurprisingly, your job is to rotate them using the face or shoulder buttons, position them with the d-pad, and ultimately arrange them into neat stacks with as few gaps as possible.
However, unlike Tetris, the object isn't to stack and then remove, but to keep on stacking, and stacking and stacking and stacking. By creating a square that's three blocks across, you initiate a combo, which you then have to carry on by adding blocks to the square's perimeter, or forming another square of the prescribed size elsewhere on the screen.
Helpfully, squares can overlap, so simply adding another layer of three blocks to the top of a 3x3 enables you to keep going, while adding an L-shape to a gap in the corner often does the same. You needn't worry about miscalculating, either, as little dotted outlines and brackets help you see where blocks will descend, and if they'll form combo squares when they do.