I have recently (March 2013) started again working with 3ds Max and here are some tools that I have developed for the 3ds Max environment using Maxscript.
Renderer Shortcuts is a control panel, where the user can adjust the most common render optimization settings, without getting lost in the panels under the default 3ds Max "Render Settings". Providing easy access to crucial render settings makes it a suitable tool for quick test renders and look development.
Easy Wiring is a tool to be able to easily create 'wire parameter' connections between the parameters of a single object and the parameters of a selection of single/multiple bject(s). Decreasing the 'click' barrier of making wire connections enables this great functionality to be used to greater extend. One additional feature of the tool is that you can also create a custom 3ds Max Dummy object that has ready-to-be wired user defined parameters on it, available to make connections with different objects. Extremely useful, if you know the value of creating complex connections in 3d scenes.
Light Rigger is a tool to have a more efficient and precise control over lights that you may create in a 3ds Max Scene. The workflow is, you choose a light in the scene and then click on the 'create controllers button' to create 3 dummies for the light, that controls global rotation, global position and local rotation. It also provides an easy access to the light that the rig is created for as well. This tool enables how lighting should actually be done; precise and manageable.
Metadata injection to EXR files is something very useful and but usually under-utilized. You can load information that would prove to be useful or even essential into exr files as the format is flexible enough to carry this information around. Common types of information that can be injected can be 'name of the file' that sources this current file, file render time, name of the render camera as well as the settings that this file is rendered with. Pretty much anything useful that you can come up with.