[loopbit]

Back in the ancient times of the early 2000's I had to deal with a massive, legacy java codebade.

I found a small free library called MaintainJ that used aspect-oriented programming as you used the app. It was great to make sense of how everything was pieced together: You coul fire it up, run through a single scenario (user log in, add to cart...) and generate a flow diagram of just that scenario.

The library still exists, http://www.maintainj.com but I haven't used it in +15 years, so no idea how it is today.