If you have followed my blog or the Microsoft Office Developer Blogs enough, you have heard over an over again how Office Web Add-Ins are truly cross-platform.
In working on a proof-of-concept I created a simplified Word Redactions add-in that is truly cross-platform. I have shared the entire project on my GitHub repository, so you can see how it works.
Here are the screenshots to prove it runs on every platform supported:
- Windows
- Mac
- Web Browser
- iPad
Word for iPad 
Word Online 
Word for Windows 
Word for Mac