He's using TextMate, and apparently wrote the appropriate plugin/bundle himself: https://github.com/jashkenas/coffee-script-tmbundle https://github.com/jashken

He's using TextMate, and apparently wrote the appropriate plugin/bundle himself: https://github.com/jashkenas/coffee-script-tmbundle https://github.com/jashkenas/coffee-script-tmbundle Command to show the JS equivalent: https://github.com/jashkenas/coffee-script-tmbundle/blob/master/Commands/Compile%20and%20Display%20JS.tmCommand https://github.com/jashkenas/coffee-script-tmbundle/blob/mas... Actual work is done via `coffee -scp -bare`, then the output is massaged and formatted for the editor popup.