iOS Simulator installed app location in Xcode 6.1
For newer Xcode's (including 6.1) follow below steps to see the installed apps (.app) location >>


Right click Xcode.app.
Go to 'Show Contents'.
Navigate to this part of the file path: Contents > Developer > Platforms > iPhoneSimulator.platform > Developer > SDKs > iPhoneSimulator8.1.sdk > Applications


Here will show all installed .app list. 

Besides if you want to install new .app on simulator, just drag and drop .app to this location.