I am a .NET developer. I have some of a problem when create a chart in .NET. I get some of Free Plot Library for chart, but I am not satisfied with speed and feature for that Free Plot Library. When searching about this library, I get a free library for this chart toolbox. I get PlotLab library. This library not 100% free, this is information from PlotLab Faq:
Do I have to purchase PlotLab?
In my opinion, this Free Plot Library running fast (I am plot more than 15000 data) and this program can show that data directly. If you interest with this Free Plot Library and want to sell your program, you can purchase this library. You can get more information about this library at http://www.mitov.com/products/plotlab
I think this is The Best Free Plot Library for NET, Delphi and C++ developer.