Among its many functions, this hugely useful plugin enables you to create an array along a path. A series of components can be quickly placed in a predefined arrangement, perfect for balustrades like the one shown above. A full tutorial can be found here, and you can download the plugin here.
One of the most ingenious plugins on this list, Helix Along Curve enables you to create helix tubing along a predefined path. When combined with Bezier Spline and Component Stringer add-ons, you can also model a perfect chain with individual links. A full tutorial on constructing the form above is available here, and you can download the Helix Along Curve plugin here. 1e1e36bf2d