3D space may have some curvature. Sfera helps to realize that.
Sfera is a sliding tile puzzle game (like the classic 15 puzzle). But its space is curved.
So its board has no bounds and is closed in itself.

Each puzzle level is initially solved. Just explore it at first: spin it, mess around, reset.
Then choose a mission (it shuffles the tiles) and try to reach the initial state manually.
Next level becomes available when 2 of 3 missions are completed.

Tap or flick to slide a tile.
Drag to rotate and pinch to evert the space.
3 finger pinch to zoom.

GPU required: Shader Model 3.0 (with Vertex Texture support).