Nagios can be applicable to a wide range of applications. They are given here −
Monitor host resources such as disk space, system logs etc.
Monitor network resources – http, ftp, smtp, ssh etc.
Monitor log files continuously to identify infra-issue.
Monitor windows/linux/unix/web applications and its state.
Nagios Remote Plugin Executer (NRPE) can monitor services remotely.
Run service checks in parallel.
SSH or SSL tunnels can also be used for remote monitoring.
via email, sms, pager of any issue on infrastructure
Recommending when to upgrade the IT infrastructure.