Tight Solutions uses Nagios        

  We monitor all customer systems internally or externally hosted. This means we know when your website is down usually before your web host does.  We perform this as a Value Added service for all of our customers because experience has shown that it pays to have the information about a downed system before users call about it. 

 We check for email server blacklisting against the spamhaus.org Zen list, catching email outages before they reach a critical level. We check for ambient server room temperature, domain name expiry date (this does happen), SQL databases, Citrix licenses in use the list goes on.