Jukebox is a collection of reusable components that allow you to create a flexible server-side and middleware framework. It features semaphores and services (not quite your usual set), a Finite State Machine implementation based on Generics, a Datastream framework (data producers, consumers and loggers), and a JDK 1.6 compliant JMX framework based on Annotations.
Nagios is a host, service, and network monitoring system that will watch your network and alert you to problems before your clients or end-users do. The system runs checks on hosts and services that you specify using plugins that return status information to Nagios. When problems are encountered, the system will send notifications to system administrators so that they can take action on the problem. The JumpBox for Nagios gives you a head start to using the system. It eliminates the complexity involved in getting the application installed, and allows you to focus on the configuration for your specific environment. Since Nagios is based on plugins, depending on what you want to do this will vary in complexity.
Just For Fun Network Management System is a PHP-based network management system that features an integrated syslog, Tacacs, TFTP configuration downloading, SNMP polling, SNMP traps, journalling, auto-discovery, performance graphs (RRD), SLAs, and a lot more. It uses MySQL or PostgreSQL as the backend and works under Linux and Windows.
LMon is a package for near real-time monitoring of logs, sending email alerts upon known (rule hits) or unknown data (rule misses). It features buffering of multiple rule hits within a given interval, cap at a given maximum number of lines, wait for a given interval before sending next alert, and auto- discovery of log rotation. It can be run from the command line without configuration, or be controlled from a central configuration file with multiple instances monitoring different log files/sending alerts to different people.
Lilith is a logging and access event viewer for the Logback logging framework. It has features comparable to Chainsaw, a logging event viewer for log4j. This means that it can receive logging events from remote applications using Logback as their logging backend. It uses files to buffer the received events locally, so it is possible to keep vast amounts of logging events at your fingertip while still being able to check only the ones you are really interested in by using filtering conditions.