Nmap is a utility for port scanning large networks, although
it works fine for single hosts. Sometimes you need speed, other
times you may need stealth. In some cases, bypassing firewalls may
be required. Not to mention the fact that you may want to scan
different protocols (UDP, TCP, ICMP, etc.). Nmap supports Vanilla
TCP connect() scanning, TCP SYN (half open) scanning, TCP FIN,
Xmas, or NULL (stealth) scanning, TCP ftp proxy (bounce attack)
scanning, SYN/FIN scanning using IP fragments (bypasses some packet
filters), TCP ACK and Window scanning, UDP raw ICMP port
unreachable scanning, ICMP scanning (ping-sweep), TCP Ping
scanning, Direct (non portmapper) RPC scanning, Remote OS
Identification by TCP/IP Fingerprinting, and Reverse-ident
scanning. Nmap also supports a number of performance and
reliability features such as dynamic delay time calculations,
packet timeout and retransmission, parallel port scanning,
detection of down hosts via parallel pings.
Read more https://packetstormsecurity.com/files/168246/nmap-7.93.tar.bz2