Gadfly is described as 'system for plotting and visualization written in Julia. It is based largely on Hadley Wickhams's ggplot2 for R and Leland Wilkinson's book The Grammar of Graphics. It was Daniel C. Jones' brainchild and is now maintained by the community' and is an app in the Development category. There are five alternatives to Gadfly for a variety of platforms, including Online / Web-based, Mac, Windows, Linux and iPhone. The best alternative is D3.js, which is both free and Open Source. Other great apps like Gadfly are Plotly (Freemium, Open Source), Matplotlib (Free, Open Source), Bokeh (Free, Open Source) and ggvis (Free, Open Source).
D3 allows you to bind arbitrary data to a Document Object Model (DOM), and then apply data-driven transformations to the document. For example, you can use D3 to generate an HTML table from an array of numbers.