Users Of Nplot
Some projects / people / companies / other I know of that use NPlot:
PolyMon (http://workspaces.gotdotnet.com/polymon) - This is a system monitoring tool that logs both status and performance counters to a database. Based on these results and various rules, defined operators can be alerted when something goes wrong. In addition, you can view historical trends of both status (frequency distributions) and performance counters (either raw or averaged).
SoccerProject Management Tool (http://www.spmt.sohosted.com) - SPMT is a standalone tool for an online game (SoccerProject: www.soccerproject.com). SoccerProject is a soccer manager game, where you have your own stadium, players, staff, etc. SPMT shows you a complete history of your team, with Nplot-graphs that visualizes evolutions of players, budget, ...
OSRE (http://quake.kuciv.kyoto-u.ac.jp/OSRE/) - Open Source Risk Engine.
BMA Coal (http://bmacoal.com) - BMA Coal use NPlot in their Coal Tracking Project
There are many, many more. This list has only just begun!