Google's Play Store is packed with some great apps, but since we're the rebellious types looking to fully utilize the capabilities of our Nexus 7s, we're going to need some 3rd-party apps—apps that can't be found in the Play Store. Don't worry, it's not some sketchy way to acquire black-market apps. This function serves conventional purposes, like getting the exclusive Nexus 5 Google Launcher on your Nexus 7. By enabling Unknown sources, we can acquire device-specific apps with ease.
Go into Settings -> Security > then check Unknown Sources. Feeling liberated yet?
Now we're ready to install third-party apps—checkout some of the mods that rely on Unknown sources