Dance.js is a simple data-driven visualization framework. It's basically a flavor of Backbone.js, but enriched with some of the ideas of the very popular D3.js visualization framework.
A Dance.js dance involves several Performers (aka views or visualizations) who are performing on screen. Users of Backbone.js might already be familiar with the API, as it's pretty much the same as for Backbone.View. Dance.js comes with its own data manipulation framework, Data.js which functions as a replacement for Backbone.Model.