Pandora FMS is an open source monitoring software under GPL2 able to work with Windows and Linux. After several months of developing and testing and two release canditates (RC1 and RC2) Pandora FMS 3.2 has been published. This version is an update has many performance and usability improvements, furthermore fixes old bugs. Pandora FMS 3.2 is available in a VMware image, RPM packages, DEB packages and of course the source code. Furthermore, now Pandora FMS Administrator Guide has 500 pages and is translated to Spanish, English and as new into Japanese.
More info in: http://pandorafms.org/
Also you can download Pandora FMS 3.2 from: http://pandorafms.org/index.php?sec=project&sec2=downloads&lang=en