Leemba is 100% open source. Check it out on Sourceforge.net .
Dynamic, real-time charts
These aren’t your parent’s pre-generated chart images.
Charts are fantastic tools for spotting trends and identifying problems, but why limit yourself to a static image that you can’t zoom? Use Leemba’s real-time charts to do performance tuning or to isolate just what happened early Monday morning last week. Compatible with existing agents
Already Nagios® NRPE and Big Brother® compatible.
Most companies will already have some kind of monitoring already installed, and it’s painful to install agents and replace firewall rules across your organization. To make it easier, Leemba aims to be compatible with as many Open Source monitors as possible.