Freshping is on to a good start. The interface is nice.
Our staff don't want awakened at 3am for a minor website going down so there needs to be:-
Currently using nodeping as it does most of the above but it's a bit "clunky" to use.
Also SMS and voice call alerts need to be built in. I don't particularly want nor have time to muck around with 3rd party stuff like twilio.