log analysis

Whats a good FOSS log analysis system? I'm after something that will aggregate the logs of multiple systems and give results on demand through a web interface and allow alerts to be propagated to a monitoring system. Also what's a good FOSS system for graphing all the metrics of a system (network use, disk IO, CPU use, and arbitrary other metrics? Ideally I'd like something like what Datadog does with a web interface that shows multiple graphs and allows easy comparing of the values from multiple graphs at the same point in time. -- My Main Blog http://etbe.coker.com.au/ My Documents Blog http://doc.coker.com.au/