A plotting tool is computer software which helps to analyze and visualize data, often of a scientific nature. Using this type of software, users can generate plots of functions, data and data fits. Software of this nature typically includes additional functionality, such as data analysis functions including curve fitting.
http://www.linuxlinks.com/article/20100518160111534/PlottingTools.html-- I've used about half of these but my current favourite is matplotlib, mostly cause I can build it into my python pipeline. I've put online an example of this for the work I'm doing on the Arecibo telescope (actually my first publication for this has been put together, a memo from the technical team :-) )
http://www.flickr.com/photos/starrydude/4630454871/