DiffEngineX is described as 'fast utility that finds the differences between the formulae, constants, defined names, cell comments and Visual Basic code contained in either two whole Excel workbooks (*.xls, *.xlsx, *.xlsm, *.xlsb) or selected worksheets'. There are seven alternatives to DiffEngineX for Windows and Mac. The best alternative is Spreadsheet Compare, which is both free and Open Source. Other great apps like DiffEngineX are Excel Compare (Paid), Spreadsheet Advantage (Paid), Synkronizer (Paid) and xlCompare (Paid).
Synkronizer allows you to compare calculation models, data bases, lists or whole Excel spreadsheets automaticallly. Differences are highlighted and can be aligned. If desired, Synkronizer allows you to merge your spreadsheets
This is a tool developed by a small team in the Netherlands. It's a standalone application that generates a simple, concise, easy to understand overview of the differences between 2 Excel sheets. It can also handle even the most complex Excel files.