App Guard by Backes SRT. The security company, a spin-off of Saarland University, offers a security and data-protection app for Android smartphones and tablets with Android version 2.3 and later for € 3.99. There’s also a free demo version which can monitor up to four apps. App Guard lets you monitor other apps and make subsequent changes to their permissions. Superfluous permissions can be revoked without needing root access.
By contrast, App Ops Starter is free but it only works on Android versions 4.3 to 4.4.1. The app starts Android’s integrated but hidden “App Ops” mode. It’s also possible to revoke individual permissions from apps without root access. Rooting your device opens up further options to monitor and change access permissions such as by using XPrivacy.
Everyone has to be clear about one thing: people who experiment with permissions can render an app unusable. Less experienced users should stay away from system services; otherwise the entire Android operating system could quickly become unstable.