For Python:

• Seaborn - A visualization library based upon matplotlib. Although not interactive, the visualizations can be very nice.
• Bokeh - Bokeh provides a bit more interaction than Seaborn, but it is still not fully interactive. 

For R: 

• htmlwidgets - Allows for tons of interaction and great for the web.
• ggplot2 - A very popular plotting system for R. It is widely used and can create just about every type of graph. However, the plots are not interactive. R visualization is a sample application that creates the graph below.

Source for picture: Science.io

For Julia:

• Gadfly - A Julia library for visualizations. Inspired by ggplot2 for R. It is not really interactive, but it is a great start. See chart produced just with HTML tags.

• Escher - Beautiful, interactive web UIs in Julia. Escher is rather new, so it is definitely a project to watch. It uses gadfly for graphics.

For more resources on Python, R, Julia, or visualization, try the data science search engine.

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