I was installing the Office 2016 Preview yesterday (link for anyone who's interested) and noticed that you can actually use the Office applications provided before the installation is complete.
When running the Office applications while the installer is still running, I sometimes see a message in the bottom right corner explaining that Office is streaming required files. I also noticed that, when running Word somewhat early in the installation (according to the installer) and trying to open the Settings dialogue, Word would hang until it had streamed the files.
How would this installation system actually work? I've never noticed it on any other applications before.