Originally Posted By: Roger
Er, .docx and .xlsx files are folders with a number of files. Seriously. Copy one and rename to .zip and open it up.

I believe this is why this feature ended up being baked directly into Windows: https://www.microsoft.com/resources/docu...w.mspx?mfr=true

I'm surprised more apps didn't move towards doing this with their documents. Though with Windows 8 "modern" apps, they also end up being zip files, named .appx: http://en.wikipedia.org/wiki/Open_Packaging_Conventions