This page contains a number of free plugins for 3dsmax. These are largely unmaintained and may not be available for the newest 3dsmax versions
Edgemap is a procedural texture plugin that allows you to draw a line along the edges of a mesh object.
The purpose of ZDeSat is to desaturate the colour of a rendered image depending
on the distance that part of the image is from the camera.
The purpose of ZTint is to tint the colour of a rendered image depending on
the distance that part of the image is from the camera. The effect is almost
identical to standard fog but has the advantage that you don't have to
re-render your scene in order to tweak the values.
TrueGrit is a dirt simulation plugin that stores its results in a normal bitmap that can be mapped onto your object using its existing mapping coordinates. The advent of global illlumination renderers in the last few years has removed most of the need for plugins of this type.