From the nmap-dev mailing list:

From: Fyodor <fyodor_at_insecure.org>
Date: Thu, 7 Dec 2006 20:19:00 -0800
Hi Everyone,
I just posted the binaries for 4.20! Woohoo! This is the first “stable” release in almost 6 months, and contains tons of important changes over 4.11. But I think you guys are well familiar with those.

Please give it a try in the next few hours if you can. Unless I hear about important problems, I’ll release it to the nmap-hackers later tonight or tomorrow morning. That posting will include a summary of changes, stupid pot smoking jokes, etc.

You can find the goods at:

http://download.insecure.org/nmap/dist/nmap-4.20.tar.bz2
http://download.insecure.org/nmap/dist/nmap-4.20-setup.exe
http://download.insecure.org/nmap/dist/nmap-4.20-win32.zip
http://download.insecure.org/nmap/dist/nmap-4.20-1.src.rpm
http://download.insecure.org/nmap/dist/nmap-4.20-1.i386.rpm
http://download.insecure.org/nmap/dist/nmap-frontend-4.20-1.i386.rpm
http://download.insecure.org/nmap/dist/nmap-4.20-1.x86_64.rpm
http://download.insecure.org/nmap/dist/nmap-frontend-4.20-1.x86_64.rpm
http://download.insecure.org/nmap/dist/nmap-4.20.tgz
And here are the changes since RC2:

o Integrated the latest OS fingerprint submissions. The 2nd generation DB size has grown to 231 fingerprints. Please keep them coming! New fingerprints include Mac OS X Server 10.5 pre-release, NetBSD 4.99.4, Windows NT, and much more.

o Fixed a segmentation fault in the new OS detection system which was reported by Craig Humphrey and Sebastian Garcia.

o Fixed a TCP sequence prediction difficulty indicator bug. The index is supposed to go from 0 (”trivial joke”) to about 260 (OpenBSD). But some systems generated ISNs so insecurely that Nmap went berserk and reported a negative difficulty index. This generally only affects some printers, crappy cable modems, and Microsoft Windows (old versions). Thanks to Sebastian Garcia for helping me track down the problem.

Enjoy!
Fyodor