Trim Brushes

From ZBrush Info

The new Trim Brushes are based on the Planar brushes but provide a different behavior based on the normal of the surface or the screen working plane. Compared to the Planar brush which are restricted to a clicked point on the surface, or a defined path, the Trim brushes do not have these restrictions by default.

These brushes will allow you to sculpt hard surfaces in a freehand way.