Very easy and affordable software which will help you minutes after installation.
E.g. you can send SQL statements against databases, trigger ICMP pings to check connection, monitor harddisk storage limit, check windows events and act according the result you get (send an email, start another program or launch a web request to trigger further actions). You can define a time-rage in which the checks are done or not. You can monitor the storage capacity and predict how much time is left until you have to upgrade. You can search for a word within a textfile (e.g. logfile) and get informed on found or not found. You have a set of very useful checks, which makes life for an IT administrator much easier.