Semonto is a Server Monitor Tool.
Semonto checks your server (portchecks, load, memory-usage, ... ) and when it noticed a problem, it will alert you via email, SMS, twitter, ...
With Semonto for Mac allows you will be able to get alerts on your Mac via Growl, a sound, a messagebox when your server went down.
An account on Semonto.com is required. There is also a free trial for 30days!
More information at Semonto.com.