Reverse engineering software

The free software tools :

nm (to list local and library functions call),
lsof (from list of open files to memory usage),
ethereal, tcpdump,... (to gather network exchange),
strace, ltrace,... (tracing syscall),
Perdr (WIN32 disassembly under GNU/Linux),
objdump, gdb,...
Fenris (multipurpose tracer, GUI debugger, stateful analyzer and partial decompiler...)

The proprietary tool :

IDApro