Oomba uses CoffeeScript
All of our Javascript code is first written in CoffeeScript for ease of reading / writing. It is compiled to Javascript before being minified and served to the client.
opening.io uses CoffeeScript
All front-end / back-end is driven by Coffeescript. For the main ReactJS functionality JSX is embedded with coffee in .cjsx files / handled by Browserify.
jflynn33 uses CoffeeScript
We like CoffeeScript because it's more readable, we use it because we have a lot of libraries and functions already (plays nicely with Rails, too)