A web based tool to produce graphs based on data stored in RRDTool, usually used as a front end for data collected through systems like nagios.
Mirror of the same bluesmoon / lognormal blog post on analysing performance data.
Cube is an open-source system for visualizing time series data, built on MongoDB, Node and D3.
Blog post from bluesmoon / lognormal on how to analyse performance data. Includes some great points on geometric means and geometric standard deviation which better apply to lognormal distributions than arithmetic means / standard deviations. Very useful.