It was a lot of fun developing UptimeButler and we learned a lot. For the actual web app we decided to give Meteor a try. The hardest part there was, that some packages contain a lot of "magic" :) But in the end, we had a pretty good feeling what we could use out of the box and what had to be done by hand.<p>For the workers which perform the availability checks, we use C# applications running on Linux with Mono. Fortunately we got into the BizSpark program from Microsoft, which allows us to launch our public beta with very little private equity.