runit - runit is a cross-platform Unix init scheme with service supervision, a replacement for sysvinit...

M/Monit - Monit is a free open source utility for managing and monitoring, processes, files, directories and filesystems on a UNIX system. Monit conducts automatic maintenance and repair and can execute meaningful causal actions in error situations.

sysvinit - Savannah is a central point for development, distribution and maintenance of free software, both GNU and non-GNU.

Zabbix - Track, record, alert and visualize performance and availability of IT resources

Supervisor - Supervisor is a client/server system that allows its users to monitor and control a number of...

Nagios - Complete monitoring and alerting for servers, switches, applications, and services