Monitor Tooling

Some history 
I did AMBI 1-2-3 in 1982, a few months before i joined the navy. In those days i fiddled with computers and stuff like that (like a Commodore 64)
I started with VAX-VMS system administrator in the 90's as part of my system engineering job on board of navy vessels. The ship sensor grid worked with two ruggedised 68000 mainframes. 
i was appointed LAC (Lokaal Aanspreekpunt Computers) and wp5  to office transition specialist 

Tools that i actually have used for an extended period of time to monitor an environment:
New Relic (Sanoma - Autotrader)
SCOM / System Center Operations Manager (Min VWS, Min. Buza)
Nagios (Municipality of Utrecht, Sanoma -Autotrader, Autoweek)
Heroix (Min VWS, specifically for the VAX-VMS servers)
PRTG - px.xom
Spotlight -  Quion.com (specific to monitor MsSQL instances)
Log4net, Check_mk (Autotrader)

Not directly tools, but ways of doing things:
MsSQL https://ola.hallengren.com/sql-server-backup.html
MOF Microsoft Operations Framework  https://msdn.microsoft.com/en-us/library/cc506049.aspx and  https://technet.microsoft.com/en-us/library/cc535377.aspx