DDD is the Data Display Debugger, a common graphical front-end for
GDB, DBX, and XDB debuggers.

DDD is a Motif application that besides the "usual" features such as
viewing source texts and breakpoints.  DDD provides a graphical data
display, where data structures are displayed as graphs.  A simple
mouse click dereferences pointers or reveals structure contents.
Complex data structures can be explored incrementally and
interactively, using automatic layout if preferred.  Each time the
program stops, the data display reflects the current variable values.