Nmap and Zenmap (the graphical front end) are available in several versions and formats. Recent source releases and binary packages are described below. Older version (and sometimes newer test releases) are available from the dist directory (and really old ones are in dist-old). For the more security-paranoid (smart) users, GPG detached signatures and SHA-1 hashes for each release are available in the sigs directory (verification instructions).
Before downloading, be sure to read the relevant sections for your platform from the Nmap Install Guide. The most important changes (features, bugfixes, etc) in each Nmap version are described in the Changelog. Using Nmap is covered in the Reference Guide, and dont forget to read the other available documentation, particularly the new book Nmap Network Scanning!
Screenshots Nmap for Mac
Video Nmap for Mac