If you haven't already come across it, diffoscope is a tool that reveals what makes files or directories actually different. It recursively unpacks archives of many kinds, transforming binary formats into more human-readable forms in order to make it easier to compare them. It can compare two tarballs, ISO images, PDF, squashfs images, etc.
Anyway, yesterday I hacked together try.diffoscope.org which lets anyone easily try out and share these in-depth comparisons using just a web browser.
The underlying idea is not only to provide a useful service, but also that it will publicise and spread the usage of diffoscope, resulting in net improvements that will feed back into the Reproducible Builds effort.
As usual, patches welcome.