https://github.com/a-laughlin/cost-per-change
For more details see the "About" link at: http://www.a-laughlin.com/projects/cost-per-change/
Also, initial description and mockups: https://github.com/a-laughlin/cost-per-change/blob/master/src/project-description-and-mockups.pdf