Xabber is available on the Android Play Store and another software repository that contains only apps that are what ?
F-Droid F-Droid is a software repository (or "app store") for Android applications, similar to the Google Play store. The main repository, hosted by the project, contains only apps that are free and open-source software. Applications can be browsed and installed from the F-Droid website or client app without the need to register for an account. "Anti-features" such as advertising, user tracking, or dependence on non-free software are flagged in app descriptions. The website also offers the source code of applications it hosts, as well as the software running the F-Droid server, allowing anyone to set up their own app repository.
AppArmor AppArmor ("Application Armour") is a Linux kernel security module that allows the system administrator to restrict programs' capabilities with per-program profiles. Profiles can allow capabilities like network access, raw socket access, and the permission to read, write, or execute files on matching paths. AppArmor supplements the traditional Unix discretionary access control (DAC) model by providing mandatory access control (MAC). It was included in the mainline Linux kernel since version 2.6.36 and its development has been supported by Canonical since 2009.