Fastscale addresses a gap in Blender's scaling workflow: while Blender offers scaling along the X, Y or Z axis within Global, Local, View or Normal orientations, scaling along a freely chosen diagonal axis isn't directly accounted for. Fastscale provides a button that starts a scale operation along an arbitrary axis, parallel to the view.
The operation runs in a single mouse drag. You click on the mesh at the spot where you want the scale to originate, which skips the need for using the 3D cursor. You then drag the mouse to scale up or down along the direction you drag, and release the mouse button to finish.
The addon was created by paleajed, who describes using it mainly while modeling art statues, though it applies to any object you model. It is listed with documentation and a demo video, and is a Dev Fund contributor entry on Superhive.