Collectd gathers metrics from various sources, e.g. the operating system,
applications, logfiles and external devices, and stores this information
or makes it available over the network.
Those statistics can be used to monitor systems, find performance
bottlenecks (i.e. performance analysis) and predict future system load
(i.e. capacity planning).
Or if you just want pretty graphs of your private server and are fed up
with some homegrown solution you're at the right place, too ;).