Hitboxes and Bone Properties
The bone tools allow you to give specific bones artbitrary surface properties, set mass bias and create hitboxes and hitbox groups.
VBSP Parser
Import Detail Sprites into 3ds Max
Import prop details from your VBSP files.
Stereo Flexes
Instructions on painting stereo weights to export into DMX.
OSL Blendmodulate
OSL Blendmodulate mask to generate a mask as with a WorldVertexTransition shader in Source.
OSL WorldVertexTransition
The OSL Shader for WorldVertexTransition.
Collision Hulls in 3ds Max for Source
Using WWMT in 3ds Max to create your model's collision hull with the Quick Hull feature.
Create Prop Zoo from VMF
Create a Prop Zoo of all the models contained in a VMF.
Starter Kits
Source Engine level design starter kits will automate some entity setups for common level design tasks.