Cscope is a developer's tool for browsing source code. It has an impeccable Unix pedigree, having been originally developed at Bell Labs back in the days of the PDP-11. Cscope was part of the official AT&T Unix distribution for many years, and has been used to manage projects involving 20 million lines of code!
Found on the TUHS mailing list
https://minnie.tuhs.org/mailman3/hyperkitty/list/tuhs@tuhs.org/thread/XORIHRWCFZKNWHB2DXNVRX7LXU4DDIZ2/