Slot-less stator in a DC motor
Slotless motors are wound in such a way that if you were to look at an individual winding, the winding would have diamond-shaped "holes" between the rotor and the outer slotless steel.  The direction of the current in the windings causes current flow on the edge of these holes to flow around their perimeter causing the magnetic field that attracts or repels the rotor magnets in the same manner as a slotted stator.  Because the winding is very flat, the gap between the rotor and the stator steel is small, so the motor geometry yields good torque, especially since a comparably sizes slotted motor is often difficult or impossible to build in these small geometries, and the rotor diameter would be small, so that the mechanical advantage would yield less torque for the same magnetic force.  For example, a slotted permanent magnet motor with internal rotor with a diameter of an inch would be very hard to wind. As you increase diameter, the slotted stator torque has the advantage.