GNU cflow
GNU cflow is a flow graph generator that is part of the GNU Project. It reads a collection of C source files and generates a C flow graph of external references. It uses only sources and doesn't need to run the program.History
It was initially an implementation of the UNIX utility cflow.cflow (UNIX utility)
cflow is a Unix command generating a C-language flowgraph.
Besides GNU, there are other implementations of cflow, like the one for Tru64 Unix.