Smashing, the spiritual successor to Dashing, is a Sinatra based framework that lets you build excellent dashboards. It looks especially great on TVs.
Written in Ruby. Has an extensive library of widgets; more can be added with SCSS, HTML, and a little Coffeescript. Has a REST API to push data to the dashboard (not pull it). Claims to have a simple DSL for accessing external data sources. Drag and drop construction. Has an extensive library of third party widgets, too.