ZABBIX is an enterprise-class distributed monitoring solution designed to monitor and track performance and availability of network servers, devices, and other IT resources. It supports distributed and Web-based monitoring, auto-discovery, real-time monitoring, SLA assurance, trending, and more.
di is a disk information utility that displays everything that df does and more. It features the ability to display your disk usage in whatever format you prefer. It also checks the user and group quotas, so that the user sees the space available for their use, not the system wide disk space. It is designed to be highly portable across many platforms and is great for heterogenous networks.
ANDReA is a LAMP-based system for registration of network clients using DHCP. Splitting the network into "boot-net" for unregistered users and a "real-net" for registered users makes it possible to gather information about users in the network. Additionally it is possible to detect active services (FTP, WWW, a game server, etc.) and unregistered computers in the network. It is mainly used for LAN parties.
Lintouch is an implementation of HMI (Human Machine Interface) or MMI (Man Machine Interface) software framework. It features a server/client architecture, componentized design, and is platform and architecture independent. The Lintouch architecture allows you to develop your own connectivity plugins and visualization objects.
OpenSMART is a monitoring (and reporting) environment for servers and applications in a network. Its main features are a nice Web front end, monitored servers requiring only a Perl installation, XML configuration, and good documentation. It is easy to write more checks. Supported platforms are Linux, HP/UX, Solaris, AIX, *BSD, and Windows (only as a client).