RRDtool

RRDtool (round-robin database tool) is a data logging and graphing system for time series data such as network bandwidth, temperatures, and CPU load. The data is stored in a circular buffer-based database, thus the system storage footprint remains constant over time.

It also includes tools to extract round-robin data in a graphical format, for which it was originally intended. Bindings exist for several programming languages, including Perl, Python, Ruby, Tcl, PHP and Lua. There is an independent full Java implementation called rrd4j.