This month, I'm still building with glibc-2.0.7. It is a very powerful, flexible, security auditing tool. Several of nmap's options appear to be aimed at not triggering monitoring tools like courtney to report attacks. As a network and systems administrator, I consider probes of my systems and networks to be overtly hostile acts. I know I'm not alone.
Required libraries are libnsl and glibc.
Nessus is a highly configurable and very powerful security auditing tool. Like nmap, it will probe your network, looking for holes. Unlike nmap, Nessus requires a graphical interface, but provides a slightly more user-friendly report. If nmap is on your system in an accessible place, anyone can run it. Since the Nessus client must connect to a Nessus server and the server is password protected, ordinary users cannot make use of it as easily.