Context: Retail versions of Windows 8 are only able to install these apps through Windows Store—a namesake distribution platform which offers both apps, and listings for desktop programs certified for comparability with Windows 8. A method to sideload apps from outside Windows Store is available to devices running Windows 8 Enterprise and joined to a domain; Windows 8 Pro and Windows RT devices that are not part of a domain can also sideload apps, but only after special product keys are obtained through volume licensing.

Question: Where can Windows 8 install apps from?
Answer: Windows Store

Question: How do devices with Windows 8 Enterprise attain apps outside of the Windows Store?
Answer: sideload apps

Question: What other devices can sideload apps?
Answer: Windows 8 Pro and Windows RT devices

Question: Where can't Windows 8 install apps from?
Answer: Unanswerable

Question: Where can Windows 9 install apps from?
Answer: Unanswerable

Question: How do devices with Windows 9 Enterprise attain apps outside of the Windows Store?
Answer: Unanswerable

Question: How do devices with Windows 8 Enterprise attain apps inside of the Windows Store?
Answer: Unanswerable

Question: What other devices can't sideload apps?
Answer: Unanswerable