The best open source alternative to Monit is Netdata. If that doesn't suit you, our users have ranked more than 25 alternatives to Monit and 14 is open source so hopefully you can find a suitable replacement. Other interesting open source alternatives to Monit are Nagios (Freemium, Open Source), Munin (Free, Open Source), Cabot (Free, Open Source) and Checkmk (Free, Open Source).
Infrastructure-wide health monitoring & performance troubleshooting in one place. Collaborate in the same place as relevant data from your systems and applications, reducing mean time to acknowledge (MTTA), & mean time to resolution. (MTTR).
Munin is a networked resource monitoring tool that can help analyze resource trends and "what just happened to kill our performance?" problems. It is designed to be very plug and play. A default installation provides a lot of graphs with almost no work.
Checkmk is a monitoring tool of servers, applications, networks, cloud, containers, storage, databases, IoT and more. Checkmk is available as Raw Edition, which is 100% pure open source, and as Enterprise Edition with a lot of additional features.
Easy to use configuration web interface for nagios and neamon. openITCOCKPIT is a perfomant monitoring system with support for distributed monitoring (Satellites), REST API, nice dashboards, maps, graphs and a modular concept for easy customization.