How to install apps on Xcode 6 iOS Simulator
The most common way to install an app in the iOS Simulator is to use Xcode to build and install it. If you have a simulator app bundle which was built by someone else (or archived), you can install it using simctl:
xcrun simctl install booted /path/to/your.app
Keep in mind, of course, that these apps need to be iOS Simulator apps, not iOS Device apps.