Common UNIX debuggers include:
dbx, which works with programs compiled with debugging information (usually by compiling with the -g option). You can also probe core dumps with dbx to determine the cause of the crash.
dbx is available on Solaris and Digital UNIX.
gdb, the gnu debugger, which is a command line debugger that can debug programs compiled on a variety of different compilers (including C and Fortran), on several platforms.