Recently I was searching for clean and simple web-based administration tool for a couple of small virtual servers so I decided to use Ajenti. It is simple and easily extendable administration/monitoring utility using Python language. Installation is very straightforward as there are packages available for FreeBSD operating system and a couple of Linux distributions.
Screenshots below are taken from simple virtual private server using Munin, Nginx and OpenVPN.
Ajenti provides a wide range of available plugins but do not worry if you can't find specific application because it is very easy to extend it using plugins. Plugin tutorial is available at developers section of the wiki.
Ajenti has low requirements and web interface is quite responsive so it is ideal for small under powered virtual servers.
If you are curious as I am then jump directly to the ng branch.