I was JUST thinking about something like this a week ago. I termed it "formula explorer" and was going to ask some people if something like it was in Excel 2013 (at work we're on 2003). This would be great for my mechanical engineering work. We often have formulas that reference many sheets with many constituent formulas. To check them I usually have to create another sheet that shows the flow of values concisely on one sheet, basically a manual version of what Slate does. This tool would automate that, looks fantastic.
