I've never tried it, but there's an open source desktop / browser-based visualisation suite called WEAVE (short for Web-based Analysis and Visualization Environment). Like Tableau, it's intended to let you explore data through an interactive click-based interface. Unlike Tableau, it's open source: you can download the source code and install your own version on your own machine which can be as private or as public as you want it to be. Don't expect anything nearly as slick and user-friendly as Tableau, but it looks like an interesting, powerful project for someone prepared to put the time in to learning to use it.
Or, you can look into rolling your own. There are some really good open source javacript tools for supporting programming data visualisation in a browser. If you don't mind coding some Javascript and some kind of server-side layer to serve up the data, give these a try:
If you're interested in the web programming option, here's a slightly more detailed write-up I wrote on Raphael and D3 for stackoverflow.
There are also some free (not open source) online datavis suites worth mentioning (probably not suitable for direct DB connection but worth a look):
- Raw by Density Design - blog introduction - (hit "Choose a data sample" to try it out) - mostly copy and paste based, not sure if it has an API that can connect to a database but good for trying things out quickly.
- Tableau Public - a free-to-use online version of Tableau. The catch is, the data you enter into it and any visualisations you create must be publicly available.
And something completely different: if you have a quality server lying around and you happen to want to make awesome google-maps style tile-based 'slippy' maps using open source tech (probably not what you're looking for - but it's possible!), check out MapBox TileMill. Have a look through the gallery of examples on their home page - some of them are truly stunning. See also related project Modest Maps, an open source Javascript library for interacting with maps developed by Stamen Design (a really highly rated agency specialising in interactive maps). It's considered to be an improvement on the more established OpenLayers. All open source.
WEAVE is the best GUI-based open-source tool I know of for personal visual analysis.
The other tools listed are top of the range tools for online publishing of visualisations (for example, D3 is used by and developed by the award-winning NY Times graphics team), and are more often used for visualisation in the context of public-facing communications than exploratory analysis, but they can be used for analysis too.
Best Answer
Boxplots were really designed for normal data, or at least unimodal data. The Beanplot shows you the actual density curve, which is more informative.
The shape is the density, and the short horizontal lines represent each data point. This combines the best of a boxplot, density plot, and rug plot all in one and is very readable.
Unfortunately, the example that you've chosen decided to add a bunch of longer lines which clutter the graph beyond recognition (for me). [snip]
EDIT: Having now worked with beanplot a bit more, the longer thick lines are the mean (or optionally median) for each bean. The longer thin lines are the data, with a sort of "stacking" where wider lines indicate more duplicate values. (You can also jitter them, which I prefer, but at least the "normal" category already has a fair density of points that jittering might make worse.)
I still think the example you chose is a rather cluttered, which could perhaps be cleared up by using jittering instead of stacking.
The paper that describes the R package for making bean plots is a nice read.