I have an Excel file with formulas in this manner:
=IF(OR(ISERROR(G16),ISERROR(G17)),X16,IF(OR(G16=\"xxx\",G16=\"yyy\",G16=\"zzz\"),Y16,IF(G16=\"333\",\"N\\A\",IF(
FormulaDesk only works on windows.
In addition to FormulaDesk above:
Here's a link to FastExcel's current Beta 3. But they seem to have been around for over a decade. $29 bucks. I think windows only. The site is unclear.
http://fastexcel.wordpress.com/2014/04/28/making-sense-of-complex-formulas-an-indenting-viewer-editer/
Similar functionality from Precision Calc. $12 Has an Nagware free version if you only need this now and then. Windows only.
http://precisioncalc.com/tf/what_is_the_formulator.html