A suite of Monitoring Plugins (formerly known as nagios-plugins)
The Network UPS Tools repository
A Swiss army knife for your daily Linux network plumbing
Performance Co-Pilot
SQL operating system instrumentation and monitoring framework
Free open source tool for real-time PC hardware sensor monitoring
Powerful system task manager
High performance ping tool
Ncurses-based monitoring application for wireless network devices
Tools for BPF-based Linux IO analysis, networking, monitoring, etc.
Leading open-source visualization and observability platform
Nagios Open Source network monitoring software - The Standard In ITM
Open Source Monitoring System for performance and availability.
VoIP SIP and SKINNY quality analyzer and packet / audio recording tool
Powerful, open-source network protocol analyzer
Intelligently block brute-force attacks by aggregating system logs
ICMP-based network bandwidth measurement tool