This product is also included in  Wall Worm Pro Pack. If you use Wall Worm, you should update WW itself and not use this standalone version.

PropLine is a parametric spacing tool that allows you to distribute props along splines in your scene. In some ways it is similar to the Spacing Tool built into 3ds Max, but it offers far more control and is non-destructive. Installing PropLine adds a new geometry primitive to Max named PropLine.

Ever wanted to clone objects along a spline? Need more control than is in the standard spacing tool? PropLine is your solution.

See the full documentation here.