QtiPlot

From the website:"As a scientist I often need to use data analysis and plotting software. One of the best scientific software I’ve ever seen is Gnuplot. It has the advantage of being free, but every one who has ever used it must admit that Gnuplot is not very user friendly. Of course there are front ends to Gnuplot, which could be a solution… On Windows systems there is a well known and widely used software called Origin, which is not free, of course. My purpose was to develop a free, portable clone of Origin. The result is still far away from it’s model, but there’s a "wish to" list which I’m constantly working on. All suggestions and contributions are most welcome!"
Find QtiPlot at: http://soft.proindependent.com/qtiplot.html