Quick list of monitoring tools
A multi-server monitoring system built on top of Salt using Django.
It can serve both as an alerting system like monit and a monitoring system like munin (using Graphite's whisper database).
It aims to be simpler, easier to setup, and more efficient than its predecessors by taking advantage of Salt for data gathering and transport.
An open source monitoring framework.
Sensu is often described as the “monitoring router”. Most simply put, Sensu connects “check” scripts run across many nodes with “handler” scripts run on one or more Sensu servers. Checks are used, for example, to determine if Apache is up or down. Checks can also be used to collect metrics (such as MySQL or Apache statistics). The output of checks is routed to one or more handlers. Handlers determine what to do with the results of checks. Handlers currently exist for sending alerts via email, as well as to various external services such as Pagerduty, IRC, Twitter, etc. Handlers can also feed metrics into Graphite, Librato, etc. Writing checks and handlers is quite simple and can be done in any language.
Ruby (EventMachine, Sinatra, AMQP), RabbitMQ, Redis.
A web interface for managing redis: cli, admin, and live monitoring http://steelthread.github.com/redmon/
A remote monitoring application using Node.js, MongoDB, and Twitter Bootstrap. http://fzaninotto.github.com/uptime/
This collections of tools allow to monitor activities and status of multiple instances of Redis server.
Twitter-bot which monitors paste sites for interesting content