Nagstamon is available in the repositories of various Linux distributions like Debian, Gentoo, OpenSuse and Arch Linux. It is also included in the ports of Open|Free|NetBSD.
Get the latest stable version 0.9.9 for Linux, MacOS X, Windows and source from Sourceforge:
http://sf.net/projects/nagstamon/files/nagstamon/nagstamon%200.9.9
Get DEB package from Debian:
http://packages.debian.org/search?keywords=nagstamon
Get RPM package from OpenSuse Build Service:
http://software.opensuse.org/search?q=nagstamon
For ZeroInstall install its latest version run this command on Linux and MacOS X:
0launch http://nagstamon.ifw-dresden.de/0install/nagstamon.xml
If you experience troube with MacOS X 10.7 you could use the fallback option to use the previous 0.9.8 version via ZeroInstall:
0launch http://nagstamon.ifw-dresden.de/0install/nagstamon-0.9.8.xml
Get latest development version via SVN:
svn co https://nagstamon.svn.sourceforge.net/svnroot/nagstamon nagstamon