Muze allows you to build complex & highly-interactive charts in JavaScript (e.g., Visual crosstab, splom) through composable layers, using a data-first approach.
Use the in-browser DataModel, along with relational algebra and data operators to create Tableau-like visualizations in browser.
Muze is licensed under MIT - so get it now!
Personally, it would be a heaven if this can be integrated with the R ecosystem.
Pros:Out of the box visual crosstab which is entry point to every viz, interaction mental model is giant, easy to create simple chart.
Cons:Only cartesian and polar coordinate supported so far.
I think it's missing things like save as image and maybe a few buttons to make it more intuitive
Pros:Looks really nice, a lot of options and you can see that a lot of effort went into it
Cons:I got a lot of the extra features like average and zooms from playing around, it's not very intuitive