Wikipedia
Observium is a Network Observation and Monitoring System (NOMS) which collects data from devices using SNMP and presents it via a web interface. It is based on the PHP programming language and the MySQL database, and makes heavy use of the RRDtool package. Observium has a number of simple core design goals driving its development: minimum interaction, maximum automation and maximum accessibility of information. These design goals have resulted in a slightly unconventional monitoring system with almost no individually customisable settings per device, and where almost everything that can be monitored is automatically discovered.
Observium is available in two separate editions: a paid subscription version (Observium Professional) with rolling releases, and a Community Edition, which is released every 6 months. An Observium Professional subscription provides read-only access to the Subversion repository, whereas the Community Edition is available by downloadable tarball. Observium Professional can be augmented with paid support services, and is available free of charge to registered charities and Open Source projects.