Android: A recent change to Google Play's permission system made it possible for developerss to give themselves new permissions without you even realising it in some cases. MyPermissions helps give you some control back.
The biggest problem with how Android handles permissions is that you only see a giant list of permissions when you first install it. You can only ever see one app at a time, so you can't see all of the different apps that, say, have access to your location or photos, without digging through the settings app.
MyPermissions takes a different approach. It will scan your system and let you know how many apps have which type of permission, and then you can uninstall them, mark them as trusted, or report them. Unfortunately it doesn't give you much more control than Android itself already does. "Revoking" permission for an app just means uninstalling. However, as a top-down view of all the apps that can access your data, it's an excellent start.
MyPermissions [Google Play Store]