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?
A: PlotLab is free for non commercial purposes. This means that you can use it for personal pleasure, hobby, or evaluation purposes. If you are student you can also use it for free for your educational needs including school projects. If you are a tutor at present you also can use it for free for your classes. However in the near future a low cost tutor license will be available, and you will have to purchase it. Your students however will not need license to use the product at class.
But, we can use full feature for this program for our research or our free program. PlotLab is a set of very fast data plotting / charting / graphing components. Add sophisticated interactive graphs, charts, plots, and waterfalls to your VB.NET, C#, Visual C++, Delphi and C++ Builder applications with minimal effort. This is a sample how look this Free Chart Library.
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.