Emerald is a personal project of mine to assist me in maintaining my small (and private) Minecraft server. I also wanted to learn a bit more about making web-based applications, so I decided to implement it with Ruby and Sinatra (a web library for small scale apps)
It is available on GitHub for public use, although there may very well be alternatives that are both easier to install and more advanced in terms of features. Still, it has proven its ability in lightweight daily use, with some field-specific extensions (e.g Kerberization)
See the GitHub repository, you can get the latest public version from there.