OpenNMS is the first enterprise-grade network management platform developed using the open source model. The three main functional areas of OpenNMS are service polling, which monitors services on the network and reports on their "service level"; data collection from the remote systems via SNMP in order to measure the performance of the network; and a system for event management and notifications.
The NET-SNMP (formerly UCD-SNMP) package contains various tools relating to the Simple Network Management Protocol including an extensible agent, an SNMP library, tools to request or set information from SNMP agents, tools to generate and handle SNMP traps, a version of the unix 'netstat' command using SNMP and a Tk/perl mib browser. It was originally based on the Carnegie Mellon University SNMP implementation (version 184.108.40.206), but has been greatly enhanced, ported and fixed and barely resembles the original package anymore.
lm_sensors provides essential tools for monitoring the temperatures, voltages, and fans of Linux systems with hardware monitoring devices. It contains a library for sensors access (libsensors), a command-line tool for sensor reporting (sensors), and a daemon (sensord). It also contains scripts for sensor hardware identification and fan speed control.
Asterisk is a hybrid TDM and packet voice PBX (Private Branch eXchange) and IVR platform with ACD functionality. It acts as middleware between the Internet (IAX, SIP, MGCP, Skinny, H.323), telephony channels (like Zaptel, T1, PRI, E1, FXO, FXS, VoIP, VoFR, ISDN, modems, Internet Phone Jack, etc.), and applications (like voice-mail, conferencing, directories, MP3 players, intercoms, etc.). It has many advanced features such as a codec translation API. The base distribution includes several channel backends, as well as applications. However, the beauty of Asterisk is its ability to be extended using its APIs, dynamic module loader, and AGI scripting interface. End users can even write their own applications that run on the system in C or any scripting language of their choice.
NASLite is a Network Attached Storage (NAS) server operating system designed to transform a basic computer into a dedicated file server. Utilizing highly optimized versions of Samba, uCLibc, BusyBox, and various other Linux tools, it provides SMB/CIFS, FTP, or NFS filesystem support. It accommodates multiple client OSes: Windows, Mac OS X, and Linux. NASLite offers SMART disk monitoring and large file support, and is incredibly easy to install and administer.