You can use any circuit design software that can export an image of your board. This image then needs a little bit of processing in Illustrator or Inkscape, from where it needs to be saved as an .svg file. The .svg file can be imported into Easel and then be sent to Carvey to mill the board.
Here is a circuit board project one of our staff made recently: http://app.easel.com/projects/j-F5zbpjKfnQfwpVYCCRKw
Stay tuned for a more detailed walkthrough of the process soon.