NmapFE is a frontend for the much loved scanner Nmap.  Nmap is a portscanner
that is able to do remote OS detection via TCP/IP fingerprinting as well.
You can use Nmap to scan a large network, or a single host.  This frontend
provides a simple GUI interface to the complexity of Nmap.  The GUI supports
color coding for various services, and enables you to append one scan to the
end of others, to create somewhat of a database of scans.