Browsing Wiki led me to
Signature Survey, a paper by Ward Cunningham. This is absolutely awesome. Amazing. I wish I had seen this before attacking the insane codebase at work. Ahh well. C'est La Vie.
Typically a browsing mechanism for large, structured programs will expose a small part of the program in response to some form of query, possibly as simple as picking from a list. However, when examining an unfamiliar program one needs to get a feel for the whole program at once. To meet this need one is better off writing a custom tool for viewing the whole program.