RRDtool

RRDtool is a much used database tool for storing performance data. It backends many monitoring systems such as Nagios, Zenoss, Monit, Cacti, and Muni. If you are a sysadmin you have probably used RRDtool.

Tobi Oetiker is the main developer behind RRDtool, as well as MRTG and SmokePing. He has a paypal wishlist and donation page located here http://tobi.oetiker.ch/wish/.