Monit is a utility for managing and monitoring, processes, programs, files, directories and file systems on a UNIX system. Monit conducts automatic maintenance and repair and can execute meaningful causal actions in error situations ::: " a great little utility that monitors your daemons "

In Short it lets you know when your Apache server goes down, when you reach your pre-determined memory usage. It will also restart key components should they stop working, for instance your web server ( apache ) might "crash" due to a DDOS attack or similar, monit will attempt to restart said services notifying you of whats going on, depending on your mmonit configuration