What are tools or techniques which well for conveying and growing mental model? Techniques I have seen which work well include:

• Building and maintaining the system (growing)
• Scribbling on napkins or gesturing next to someone with a furrowed brow (conveying)

Documentation which enumerates surface area or catalogs features may be exhaustive but often doesn’t achieve either building or conveying the mental model of the subject in question. Using a well designed tool or product directly can achieve both. What are the tools and techniques which work for you? What makes them effective?