I've always wanted a runtime visualizer, and/or a static analysis visualizer. With a couple of exceptions I was unable to find a suitable library and it seems for some reason this hasn't been built yet.

So I also decided to take a stab at this, and hopefully will share if I get anything useful. I'm using Haskell + Diagrams to construct a JS parser (to begin with) that will do static analysis and render a graph of whatever you need. The simple use case I've always wanted was just a slice of the graph of the function calls, perhaps with some information on context variables. Seeing this visually would help me get up to speed with any codebase and would allow extremely fast contributions.