I implemented an offset module in RapCAD a while ago. I developed it primarily for calculating print outlines, since the outline must be smaller than the required shape by half the width of the printed filament. The module can also be very useful in other applications such as creating a hollowed out shape. Usually we can create a hollowed out shape simply by performing a difference operation. However when the shape is complex it can be tricky to create a smaller shape of the correct proportion to subtract. 
In the above image the top 2D shape is created using the offset module, whereas the bottom shape is created using a naive translate and scale technique. Where the scale module simply shrinks the shape uniformly in all directions, the offset module shrinks the shape to the correct proportions offsetting the outline of the shape by the same amount at every point.
Version 0.9.0 is available this month. See the Download Page for details.
Giles Bathgate 