Webapps are often built and managed by single person or small teams. For example, I run 11 sites and web apps, just in my spare time, on one virtual server. I need to know if that server is up. We need a lightweight, low/zero maintenance way to monitor applications and servers. Mainly we are concerned about presence of our application. Is it there ?

Where else does presence matter ? Why, in Instant Messaging applications of course. Currently we record presence of our friends in our messenger clients. Well, servers can be our friends too !